This is one thing I'd like to understand more.
Personally, I don't see low transfer prices on high salary players as a problem. That number alone does not reflect the total value of the player.
I see what you mean. And I agree with that somewhat. I get why people aren't bidding on players like that as I am not doing it myself. There are probably some cases when like you said some players are still valuable but usually it's not the case.
And I see why and it are reasonable economic decisions. But like you already said, training a player costs money even if you don't take into account the players salaray it's an easy 50K a week for the first to seasons and 25k+ a week after that. And that is cheap while not including the buildings (because you probably don't NEED them to build a good player to sell).
Some managers want to train players to make a profit so they can build on there savings which in the future they can use to make a contender. And I think that a change like this one were the players salary gives back a percentage of money will help manager to turn a profit on their trainees easier. Especially when they train them for longer and max them out.