I've spent twenty years in higher ed and feel like this article is missing some of the macro elements at play. Around 2008 during the great recession state budgets were shrunk and in turn, state funding for higher ed was cut. The costs were offset by reducing costs and raising tuition. This trend has continued since then in varying degrees where states further reduce funding and tuition increases. So of course tuition revenue is increasing as other sources of funding decrease. The fact that it corresponds to decreased attendance means that the rate of tuition increase per student is greater than the rate of student attendance decrease.
The article also doesn't cite the exact details of their data sets, and I clicked through to there sources but couldn't confirm what they included in enrollment numbers. E.g., did they include non-degree seeking students, continuing education credits, etc? Did they isolate for increases on degrees or graduate degrees that have always cost more per student? They might have, but don't share their work if they did.
So is it a problem that many schools are chasing rankings at the expense of affordability and accessibility? Yes. But I'm not sure they presented the data in a way that supports their specific claims. What they need to do is show the data broken out by student and degree type.