I think the author is reversing cause and effect and so not coming to a terribly useful conclusion. It rather seems to me that fewer men (proportionally) are attending college because the value proposition has substantially declined. Similar things have happened in many other careers formally dominated by men.

In some cases this is simply due to oversupply leading to declining salaries. For example decades ago a Bachelors of Philosophy would qualify you for a number of high paying jobs. Now it qualifies you to be a checkout clerk. You can't expect to approximately double the number of candidates without reducing wages.

In the particular case of college it's been ever more clear for more than ten years now that college is mostly only valuable if you treat it as a trade school (ie. BSc of CS into software development), if you need it for immigration purposes (eg. the booster Masters), or if you are part of the academic or political elite where a PhD or two is table stakes. For everybody else college costs too much in time and treasure for the employment advantages.

In other cases the underlying market has changed. One interesting example of this is Science Fiction writers. Starting about a decade and a half ago a ton of mid-career mid-listers who wrote science fiction switched to other genres, mostly mystery, because the market for SciFi kind of dried up. You see many more female writers in SciFi than you used to, but they don't make the same kind of money SciFi writers would have thirty years ago -- the money simply isn't in the genre anymore.

If you look at the authors examples I think most of them fit this latter case. Being the tutor to the scion of a business magnate is probably just as good and competitive gig now as two hundred years ago, but 'teaching' as a market has filled out immensely since then and is now at least 25% day care -- something which cannot be prestigious because it is common and cannot command large wages.