In all honesty, United don't have very much to attract top talent to the club other than money at the moment. The traditional reasons for a player wanting to join a club:
Manager
Ole isn't as experienced or as a much of a draw to our club as other managers are. Zidane, Pep, Klopp are objectively better managers.
History/Legacy
United may have the best history, but that could be sen as more of an albatross than a blessing for many potential signings because why would they really have the desire to help United reclaim lost glory versus helping another club cement their own legacy?
Champion's League Football
This is most certainly a big one for elite talent. Ole and Co really screwed the pooch on this one messing with tactics too much at the tail end of last season and failing to qualify for Champion's league. Ole increased his chances of getting sacked next season by about 40% by failing to qualify.
Clearly defined footballing hierarchy/structure
Some players may not care about any of the above, but might enjoy a highly regimented training system and clergies delineation of coaching/players/management. Basically the feeling of a "well-run club", I don't think United would illicit this feeling at all. It's seems clear that player-power runs rampant at United, and I'm not sure potential signings who are most dedicated to just playing football would appreciate this at all.
Great players to play along-side
Speaks for itself really, we lack any players that are truly world-class/legendary or have the potential to be legendary.
Inspirational Captain
Failure in having many world-class players, maybe we could have a single very good player, who is a inspirational in the dressing room and could potentially assist in attracting new talent, but at United, all you'd see is Gashley-fecking-Young with the armband.
Nice City
Let's be honest, Manchester isn't a very nice city at all. Even Liverpool is a nicer city, just down the road. Maybe this is subjective, but how many times in the past have we heard of players being OK playing in London or preferring to stay in a sunny-clime? This one is obviously out of the hands of United, but it's still a factor.
Chance of silverware
United have basically zero chance of winning the league next season, aren't in the CL, and don't really have the bottle under an inexperienced manager to have potential as a solid cup team.
So, in summary... I think we're pretty much fecked. The above points are just things that I imagine a potential signing would take into account when accessing any club, but with United, based on its recent history, the problems run even deeper than just what I've just listed. There are far, far, far better options than United at the moment. It's very sad and I love Ole, but the fact Young, Jones, Smalling are not only still here, but got new contracts speaks volumes about United's ambitions going forward and if I was in a position to make a decision whether to join United or not, for myself or maybe my son, I would avoid them for now. Very sad.