In my anecdotal experience in a FAANG, weak junior hiring started during the hiring freezes in mid 2022, and was made worse by the layoff cycles that began soon after. Once you know headcount is going to be extremely tight indefinitely, you want to use your precious few slots to hire someone that can deliver value pretty quickly, rather than take years to coach up.

It personally seems hard to connect that to remote work as that had been going for 2 years and in between was the largest hiring burst we'd done, which included many junior folks. Though admittedly I'm biased as a remote worker.

And this is why people do studies, because anecdotal evidence is a hypothesis at best.