A point that could be discussed endlessly because there are so many ways to look at it. I would like to note that by not looking at what someone actually makes you remove that particular incentive to hide income and you remove that particular disincentive on becoming wildly successful in spite of the lower-paying degree.
It's also worth pointing out that the higher-paying degree holder still generally comes out way ahead over a career-length timeline.
That would just incentivize people to pile onto the perceived high value programs like when everyone got into CS during the first dotcom bubble. Not a fitting solution for an institution intended to develop capable members of society rather than just making money.
Your comment would only make sense if higher education institutions didn't evaluated students throughout the whole degree. If a school ends up graduating individuals that are not capable members of society then clearly the problem is not how many freshmen enrolled in a course.
I honestly don't know anyone in my (australian) high-school cohort who even thought about the varying costs of under-grad degrees. It's such a small difference, and it's all covered under HECS anyway.