It's all too much at once. It's a hard thing to do but the coach and recruitment have to know how to slowly remove and replace the key players. Fergie was a master at it, he kicked out a bunch of those 90s players over a few years, Beckham, Keane, Butt, and Neville, were all replaced over three years. Barcelona is kinda doing a good job of it now, Messi, Xavi, Iniesta, Pique, Alba, Alves, Busquets, Puyol, Suarez, are all gone from the club. They maybe hung on to some too long and others not long enough but they've had huge job replacing those players.