How do you decide what majors are useful or not? It seems too arbitrary. Many people also don’t necessarily use their specific degrees, even if going to college itself was necessary. My dad was an English major, he now works in supply chain management.
You create a quota for the different majors based on the employment opportunity for the individual majors.
College should not be a jobs training program for employers too lazy to do it - and the people who need free college are not the ones who are going to economically benefit from it. We should be subsidizing the people who have valuable interests that are important to study but who will not otherwise be compensated for it by the market.
The 'employable' majors should be paying full sticker price. They can afford it.