We seemingly are incapable of buying anyone so I'm not about to get picky because of agents...
In all seriousness, yeah Raiola is a dickhead, but hes just doing his job. Pogba also would have no problem staying if we were doing well and competing for trophies. We've just gotten worse and worse though since he came, and now hes at the point where he needs to move while hes in his peak to compete for top trophies, and not miss out on them because we are going from one turmoil to another.
I said it before but I'll say it again. Giggs and Scholes are United legends who played their whole careers at United. Rooney stayed for all his peak years as well. As did Keane, Rio, Vidic, etc. None of them would have stayed all those years if we weren't fighting for trophies regularly, or maybe just 1 at best. Liverpool keeping Gerrard for his career despite not competing for titles, Roma with Totti, etc, that's incredibly rare. Top players will eventually move on to top clubs to win trophies. And there really cant be hard feelings about that.
We all blame Raiola, but it's only logical. We somehow managed to keep De Gea through all his peak years and now hes declined where its not a problem keeping him, but that's a very rare case (that we lucked our way into).