Because, Z, you just named 9 players of a squad of 25, and said you still missed some. ****, even FM punishes you for clearing that many players in one go. Honestly? I'd give Pereira and Young one more chance. Periera is still very young, and Young offers a lot of versatility, and honestly, hasn't been half bad. Plus, McTominay, give him a loan and see - too early to be writing him off.
Point is, even Dressing Room presence matters. The reason why Valencia is still important, and needs to be kept happy is that he is a significant figure in the Dressing Room. And the atmosphere there impacts games lot more.
Don't get me wrong, we need to clear the dross, but you can't just dump every player out, and replace them all. You need backups, you need rotation. And youth can't immediately come in and be rotation. It's the ideal scenario, yes, but not always feasible.