This is my point. Lots of positive plaudits.But he doesn't score goals.
Man Utd should not be some 'community' club, helping players feel better etc. You need to embrace being a Man Utd forward. That's not me, that's just the history and expectations of the club.
Zirkzee seems to be a little lost as to what should be expected of him. I suppose, in his mitigation, he is not the only player going through this.
I mean it's normal if you're contracted as a link-up option in CF and then - ignoring necessary time for adapting to a new environment in general - but then asked to be a direct striker that it either will take time or means a mismatch.
That's not Zirkzee, that's the current management, both of the club as a whole and the field staff.
So, it's kind of a question of why get a player like him and then ask him to be someone else? You can ask anything of a player, of course, but whether your question gets a desirable answer has to do with more than just the level of a player, or the level at which the team/club wants to play at (eventually).
If the other players were more proficient and better at linking up, perhaps 7 goals would still be low, but if "the eye test" shows he is a part of dominating the side or set ups of goals, it would be considered a non-issue.
Now that Hojlund, Garnacho, until relatively recently Bruno, etc. haven't attributed goals to this side, suddenly a Zirkzee type seems a lacky striker, even though there are plenty sides where he'd be a great fit, and even addition to what they were already capable of. But while it's fair to ask for more result and development from his side, it's unfair to say he's doing a bad job when you ask an apple to act as an orange. Benzema didn't score much when the focus was on supporting Ronaldo, and luckily for them managed to develop that side later, but Benzema was still an amazing and important player before he became their main goal threat.
Seeing Zirkzee already improve so much in areas he wasn't signed for, why judge him for things that weren't his (main purpose). The whole team (relatively) stinks, like you said many players are going through this. They don't suddenly stink themselves, that's why many shone before they signed and are showing at least a higher level after they left, too.
United shouldn't be anything, but any employer is at least partly responsible for their employees, not only for their personal wellbeing, but healthy human beings are also generally speaking the more efficient ones. Otherwise stuff like "people manager" wouldn't be such a big term in football, either. Especially if you get in a young player it would at least help to try to make them feel better. But the club/board do need to figure out a way to get themselves out of this mess. Currently their history is more a thorn in their side than a benefit. The last years have shown that the higher end finishes were (and become even more so) the outliers than the subtop finishes were. United is not a top club right now and everyone who expects them to be at this time is delusional. Now you have Amorim saying that they fight for the title, because he saw what happened to this predecessors willing to admit United is not ready to dominate any time soon. Amorim needs a whole lotta luck to come even close to achieving his words. Hopefully he's lucky enough to win this EL so fans can continue to tell themselves that United is a club with big expectations.
If you're realistic you expect the current United to finish around 4th-8th place and their youngsters to be inconsistent. You're a horrible manager if you get some young adults and expect them to have the composure and output of a seasoned star. Whatever you want as a fan, the club has decided to go for "projects" with these youngsters and I can't think of many projects that began as finished products.
I expected more goals and assists from Zirkzee, too, but he isn't first player to underwhelm in his first 6-12 months. And that's at a stable club in an at least relatively stable team. So if anything, his more recent performances are better than what I expected in December-January. If he doesn't grow further, sure, you win. But if you want to get an instant success, you do a Galacticos. Currently, this club neither can nor (seemingly) wants to, as their "history" is also turning rookies into champions (yes I like Digimon, too). That's why Mainoo and Garnacho, and occasionally Amad and Hojlund, were fan favourites last year. They were far from good enough to star a top side, but they did show a type of promise that got people thinking there might be a bright future ahead again. Just like Rashford, Greenwood, Martial, Shaw, and more did before them. Since it's Manchester United and Real Madrid, while you can expect the manager and especially the board to do better, the promise of Zirkzee recently is almost exactly what you can expect at this club. The only thing that turned players like him into "what's wrong with this club" is that the players, at least the experienced players around him either don't perform or don't exist. If someone else is better, you move on from Zirkzee, but currently "what's wrong with the club" is that it's all a chaotic mess beyond any single of its players.
So far we've seen that the failure players were often not terrible after they left, while the club continued its steady downfall. So by now I'd think it'd at least make sense to not single out anyone beyond being a possible misfit. It's exactly the same for players like Garnacho (or Amad, Mainoo, etc). He didn't suddenly lose his talents, but you can see he's a direct wide player with a tendency to be selfish, but with a decent/promising finish. But expect him to be a 10 and suddenly his runs are often useless, misdirected and you miss a more creative playmaker in your more forward areas. You might get a similar result if you expect Amad to focus on being direct, though he seems to be a more adaptable type of player. Zirkzee doesn't look like an Amorim player so far and I don't think we can judge any player on the first few months of this season, especially the new ones. Honestly I am surprised Zirkzee is moving closer to what Amorim wants from his players/strikers than Hojlund managed to do. But if they stick with Amorim I still think it might be best for both Garnacho and Zirkzee to look elsewhere. Not because they cannot meet the expectations for the club (incosistent players who might show better things later is exactly what I expect from this club no matter what coach leads them), but, if you'll allow my amateur scouting, because they don't fit the direction (of playstyle) this club and manager has decided to head in.
Excuse my slight hyperfixation leading to all this

Feel free to pass by it if not interested in all that. Part of who I am, but aware it's not part not of all of us
It is also his first year at the club and he changed coach part way through and is now injured. I think it would be entirely fair to criticise him if he has a disappointing goal tally again next year but in the meantime appreciating the qualities he does have, along with the fact he seems to have improved through the season, is important. It's not like we can change every single player who has disappointed this year and for me his progress is worthy of a bit of a grace period.
Plus I think this basically functions as a TLDR-summary of sorts