I’d guess the simple answer may be that people don’t care/know, but for those that have ditched Facebook for whatever reason, yet still use Instagram, it’s a little surprising.
Is it partly a result of it being a more focused/limited form of social media that filters out some of the stuff people didn’t like from Facebook?
It’s funny in a lot of conversations about RCS WhatsApp users (mostly from outside US) make fun of RCS fans as if WhatsApp is not owned by a multinational corporation!