Why doesn't Uber just let Californian drivers set their own rates? Would it really be such a huge deal to their business model if drivers could set their own pr

Why doesn't Uber just let Californian drivers set their own rates? Would it really be such a huge deal to their business model if drivers could set their own price per mile, or similar? Uber still takes a percentage cut and I assume the free market cost would work out to be in the same ballpark as Uber's pricing model.