I joined linkedin because it seemed a reasonable way to manifest myself as being an actually employable person, in particular, being able to build a graph of the people I know (and know me) and write/receive written recommendations. Not so much for the recruiter stuff, but my profile there gives me a bit of additional credibility, that, at least other people who know stuff, say that I know stuff too.

I'm very much not looking to join any "platforms", I don't consider HN a platform, but for instance Mastodon, which I recently lost all respect for, I didn't have to leave that though, I was kicked out (for saying that people shouldn't be discriminated based on the color of their skin, on a BLM+LGBTQ++whathaveyouallthewokeness friendly server of all places).