Why? The reason the contract, made before school works, is that it reduces risk. You don't know which students are going to end up rich and which aren't, so you have to deal with them equally. So a percentage of income is fixed at that time, and everybody is happy. Your premium for incurring this risk is a higher price (higher percentage of income). Which is still far below what students are willing to pay before college to get rid of that risk!
If there's no contract, the whole thing is eviscerated.
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Congratulations to SuperNiceDog, Guru Winner, who was smart enough to pick
your 7 time champion, Link.