People in Iran or China don't rely on Facebook and Instagram. Before Facebook penetrated Europe in ~2010, each local market was dominated by copycat services like StudiVZ or Hyves, which then vanished within 2 years. When the US floated the idea of banning TikTok, some people felt compelled to download Chinese social media apps.

If a country was to ban Facebook from operating in their country, people would be on an alternative 2 weeks after. There are reasons why a Facebook ban would be hard to enact, but dependence on the product is not one of them

This may sound weird, but: Alternatives will appear, just like how Chinese people have been able to live their lives without access to Google, Facebook, Instagram, YouTube, WhatsApp etc. The alternatives may not be good -- I'd argue the Chinese version of Google (Baidu) is quite a lot worse in many ways -- but they work and are good enough for most people.