It would incentivize them to only offer majors that lead to high incomes. By pooling the money it removes that issue.
If everyone gets major that leads to high income, market will become oversaturated quickly
.5% of income over lifetime of alumni is very long-term investement
Universities are well aware of that and obviously won't self-sabotage in such dumb way
More likely outcome is that universities will ensure that most talented students will get high income majors
jobs that pay well are a signal that there is high demand for this skill in our society and that more people need to develops these skills.
Why would we not want universities to respond to that signal?