Lewandowski is in the last year of his contract, so it's obvious why there may be a transfer. Silva could leave but the reasons could involve the following:
1) High wages but missed a lot of games so PSG may decide to look for a different option.
2) New France tax regime.
3) The PSG owners may decide to downsize their plans(like happened with Malaga last season) maybe even partially because of the new tax laws. Maybe because they see the Champions League out of reach(Barca was bad enough, now Bayern look immense). Maybe also because they are looking more seriously at complying with FFP.
4) Maybe Silva wants to force a move, PSG may decide it's not worth keeping an unhappy player and the funds they receive for him can be adequately used to improve the squad.
1) High wages but missed a lot of games so PSG may decide to look for a different option.
2) New France tax regime.
3) The PSG owners may decide to downsize their plans(like happened with Malaga last season) maybe even partially because of the new tax laws. Maybe because they see the Champions League out of reach(Barca was bad enough, now Bayern look immense). Maybe also because they are looking more seriously at complying with FFP.
4) Maybe Silva wants to force a move, PSG may decide it's not worth keeping an unhappy player and the funds they receive for him can be adequately used to improve the squad.