I do think there are enough people who think (sometimes wrongly!) that they are acquiring valuable skills in the classes, but at the same time, I don't think they're a majority. Or at any rate, if you actually asked people to reflect, they would probably realize that they're not learning valuable skills.

Last year, I was teaching a linear algebra class and held an extra optional class on a holiday (I actually offered two holidays where I offered parallel versions of the class) covering some aspects of linear regressions, which is the most important topic of the course. From the human capital perspective, it's the one class people should have been interested in attending (and I had made them well-aware of this fact). In total 6 of 30 students showed up (4 in the first slot and 2 in the second). About 4 more said they wanted to come but couldn't make it. The next time I taught the course, I made that material part of the regular course, and of course everybody showed up to the classes and mastered the material and did well on the test. From what I've gathered, the numbers I encountered aren't unusual: when one holds extra classes on highly relevant material, it's unlikely that more than 20% of the people will show up. That 20% is still a lot, but it's not most people.