Everyone has already seen that United is a swamp, so it will be extremely difficult to lure any promising player there (not to mention top players).
This is an extreme exagerration. Joining Manchester United is still far better tha joining 95% of the rest of the club around the world and thats a fact. Although Manchester United is currently not in any way potentially to win any of the top trophy, its still a pretty good club. The only reason why it seems like we are pretty bad right now is because Manchester City with Pep is over dominating the league and not to mention that currently Liverpool is pretty good as well
Pep Guardiola, Arteta and Klopp are more experienced and dominated altogether top places these years. Not only their contributions driven their teams to that but also the contribution of the owners that offered top players and reinforced considerably the squad.
Manchester United are suffering from the inconsistency of the results although having good players and coach since the tactics used and the mistakes of the players are too much to maintain positive results. If there is something particular for Manchester United and Chelsea, is the money spent to purchase players and these signing turns to be overpriced and useless in many cases.