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?
Probably because it doesn’t fit the vibe of Meta. Lots of influencers use it so people just don’t care and don’t need to step back and look at the bigger picture.