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?
I second this opinion as well, FB back in the day was for youths, then… My parents were on it. And the entire neighbourhood and their dog, too. I have a limit on how much crap I can see in my feed. Slowly but surely I left it.
Instagram filters out anyone who doesn’t care for visual content. And it didn’t start as part of FB.