It's slightly different than that.

It's the low "cost" of publishing a job post to various boards, and the low "cost" of applying to jobs that are posted.

The combinatorial math has exploded the number of applicants per position, but the talent pool has not expanded by that much.

The net result is companies are abdicating agency to ATS systems in an effort to filter the "best" resumes.

Candidates are responding by feeling disillusioned by the ghosting, non-responses, and 400 applications within 24 hours to any new job posting.

PhD positions (at least in the UK) are similarly in demand: about 100 applications for 5 places. And, inspired by your calculation, it’s definitely not true that each person is applying to 20 places. I guess a lot of people just don’t get in. It does seem like a lot of people I know are genuinely struggling to find a job.

There are probably more than enough lower paying, lower prestige jobs on offer, but they don’t require academic qualifications and so university graduates feel they deserve better.

A lot of job sites make it easy to apply to arbitrarily many jobs, so if a candidate wants to they can fairly efficiently apply to every job on the site. It's not hard to imagine that there are at least 200 such people.

I don’t know. They are remote positions so there are a lot of geographies that can apply