You don't recall classics like this from last season? I remember it happened against Bristol the game before too!
I haven't even watched United a lot, and I've seen this happen a lot from the the said players (especially Rashford).
I can also recall "classics" when they do feed Lukaku, including Rashford in the 1st half of the season. Rashford clearly lost his way a bit as the season wore on (seems like he's trying too hard to imitate Ronaldo
), but claiming that he wouldn't "ever" feed Lukaku due to some lack of "respect" is, I believe, revisionism based on his poor 2018.
Sanchez's problem seems to be more that he hasn't figured out his role in the attack yet, rather than simply being greedy. It's not like he's been shooting loads to try and claim the glory for himself. He did also assist Lukaku's goal against Swansea.
Lingard I can't remember specific examples, but he generally doesn't shy away from feeding others. Could fault him for quality but not for selfishness.
In general the whole United attack is just guilty of poor decision-making.