First reaction:

Sometimes real world players will take contracts just to be with a "winning team". They want another champions ring on their finger, haha.

Application of this
1) some number of high quality players currently on the winning squad have contracts auto extend. It's basically cash, and advanced managers may prefer to sell, so it won't always be an advantage. But for some managers helps keep the squad.

2) winner of a title is shown a set of recommended players that are a bit better than regular recommendations, or are free/ cheaper. 3 players, pick one.