They 'solved' this problem by introducing collections. basically, the more players you own from a specific team in a certain year, the higher your collection bonus % will be for that team up to 5%. It gives a reason to buy cards of players that no longer are active.

In the end though they will turn worthless which is part of the game I would say. It's already hard to allow players to have a use case in the game their entire career potentially. It's also the reason why older players are cheaper and younger promising players are often more expensive as their lifetime is longer.