And a positive EV isn't sufficient. It would also need to have a very low chance of negative EV. Otherwise people would be crazy to sink $400,000 into a degree that might or might not leave their child with better job prospects in the future.
Of course, only the wealthy pay full price for college, but when you ask people if college is worth the cost, they may be anchored to those prices even if their own kids would end up paying less.