It's the professors who are interested in doing all the other things professors do but regard teaching as a chore that have problems with under-performing students. They put in less effort into teaching (why wouldn't they, it's less important to them) and it shows when the lower quality students fall through. That doesn't mean they're not good professors, they just aren't good teachers. I've known some really great professors that I would never want to take any class from because they didn't prioritize good teaching and likewise sucked at it. Undergrads and these professors would probably be happier if schools relaxed the teaching requirements for this group but that has other trade-offs.
As the price of college has increased the amount of extra work (office hours, Q/A sessions before major tests, etc.) professors are expected to do to prevent the customer from failing and having to spend thousands to go around again has increased with it. This is independent of student quality. The author sounds like he/she is annoyed with the new normal and is blaming it on the few people who bribed their way in. In reality student performance in any given class is going to depend mostly on how much they care. If you're teaching some elective that checks a certain box for a large group of undergrads and sounds like it's easy but is really a lot of work you're gonna have a lot of students barely passing, even the smart ones because your class simply isn't a priority for them.
These things aren't the fault of students, professors or any one group, it's just how the complex system that is college education in the US has evolved.