Trump is about to be President. He can't have something like that hanging over his head. It's not fair to him and it's not fair to the American people. This was a good resolution to put it behind him and get to the important business of running the country. He has more important things to do now.
First of all, he's getting a tax write off for the settlement, so his actual cost will be less. Secondly, there are a lot of folks who spend upwards of $35,000 and received little or nothing for their money, and it's not likely they'll all be made whole. He's not admitted that his uinversity was essentially a scheme to defraud people. Finally there's some question as to how Trump will pay the settlement and he's been known to misuse charitable funds before.
Many people argue that this amount is insufficient, as the possible outcome could have resulted in far more money. However, the parties in the lawsuit agreed to the settlement, and they are the people who count. If they feel that the amount is sufficient, then there is nothing you or I can say to change it.
$25 million dollar fine is a sufficient solution for the Trump University case. In fact, it should be $0 because people were fully aware of what the University is yet they proceeded to take the course anyway. People are no longer required to take responsibility for their actions. If something goes wrong, just sue.