There have been two midfielders bought by Manchester United in the transfer market this summer, Cristian Eriksen and Casemiro.
While other clubs are targeting players who are still in the golden period, Manchester United actually brought in players 30 and over 30 years old.
So what about the others?
Seems you're forgetting Manchester united are playing in Europa and not the champions league, players are likely not going to be interested in playing for Manchester united especially the big names they're chasing. Assuming Manchester united were playing in the champions league the they would had have a chance at signing youngsters but since they aren't then they have to settle for what they have now and it isn't that bad compared to previous seasons.
Before, the Manchester united midfield was occupied by Scott McTominay and Fred meanwhile Bruno Fernandes was the only quality player among them and that was killing Bruno but now he has other qualify midfielder as Christian Eriksen and just signed Casemiro. With this midfielders Manchester united can control the game against smaller clubs to build confidence in challenging the top clubs and secure a champion league next season.