Given that I see nothing for "react" on jobs.facebook.com listed by Facebook for my job market, I still don't see how Facebook could be relevant to that part.

But, if Facebook actually hires react engineers everywhere and just doesn't like their own job platform, then they probably hire php engineers everywhere as php is the platform they are the most famous for sinking money into modernizing.. So again, I'm left to wonder why anyone who already knows php would be told to learn react before looking for a job.

It's a lot like always being told to learn Ruby on Rails a few years back even if you knew nothing at all about ruby. I wonder where all those ruby illiterate RoR engineers ended up.