Yeah, but after tenure...

that's the real problem. "Tenure" as such takes care of (at most) the first ten years of a thirty year (or more) reign as a professor at an institution. That is another thing to watch for in quality undergraduate education (as opposed to merely "elite" in brand name, I mean)-- are SENIOR faculty, on average, the ones in undergrad classrooms? Or is it only a few of them, mostly those who haven't published anything in 20 years either?

Which undergraduate classes are being taught by faculty, and which operate as their own entities, with separate faculty who do nothing else, and run a stable of adjuncts/TAs to staff them? Largely it's service courses that operate this way-- in Math, it's Calc, in Chemistry, it's Gen Chem, in Physics it's Gen Phys, etc. Those classes tend to be more or less similar from one institution to another, and only rarely are really stellar faculty the ones teaching them-- most often, it's someone who specializes in that course. Almost every large institution has those people. If they are good at what they do, you should see fair numbers of majors-- about one junior undergrad per faculty member in the department in something like chemistry or physics-- and if they are total trolls, you'll see far fewer majors than expected... or you'll see a parallel system in which the majors aren't in that "machine" with the rest of the students who need the course.

Those are the data endpoints-- all I'm doing is describing a mechanism. Most classes that are numbers-intensive like that, they don't want the department's own majors getting lost in them. On the other hand, some places figure that if you have the right stuff, you'll make it through and they'll see you as a sophomore. Different kind of environment, though. DH went to a large state flagship in CA that operated that way.

Schrödinger's cat walks into a bar. And doesn't.