One thing that's potentially different, at least for Facebook, is the network effect. It only takes a few friends to start using Facebook for event planning for people to start missing events or worrying about missing out. That extra pressure cuts against individual choice.
Instagram is different, but you can see something similar happen on platforms with a chat feature. If people start to gravitate towards a singular app for talking, coordinating, etc. then there's the potential for resisters to be socially excluded. For most people, feeling socially excluded is a strong motivator. So far, this has mostly resulted in everyone having a fairly broad set of apps with chat features, so I'm not sure the centralizing power is as strong.
Hey nice to hear somebody taking about social feature of a social network when so much of this is about profiling people through infinite scrolling content from strangers.
It'd be hilarious to see the EU demand interop on features like Events, Groups, Marketplace.
The overwhelming majority of local businesses around me don't have websites, just a FB page. If you want to look at upcoming events, specials, restaurant menus, etc. you either have to hope FB doesn't throw up the "you need an acct to see this page" blocker, or sign up.