I see it mostly with very small businesses and government offices, especially in small towns or rural areas. Years ago, they might have employed someone part-time to maintain their domain name, server or hosting service, website, etc. Then it became free and much easier to just create a Facebook page, and any layperson in the office can manage it as the social media coordinator. Sometimes they still have a real website, but it hasn't been updated in years. All the recent and relevant information is on their Facebook page.

There was an item on Hacker News a few months ago about the crisis of water contamination at Pearl Harbor in Hawaii. As commented on that item, I was there. For a while, a couple Facebook pages were the only sources of timely information for affected residents. All the town hall events, in which US Navy and Army officials answered questions, were streamed live on Facebook, and being logged into a Facebook account was the only way to ask a question if you couldn't attend the town halls in-person (which had limited seating due to COVID). It was probably two weeks before they started putting all the information onto an official non-Facebook web page after people complained about this (during the Facebook town hall events, on behalf of friends and neighbors without Facebook accounts).

People have a really weird definition of "need". Nobody needs Facebook. A handful of things might be moderately more difficult without Facebook, but not impossible. I bet if Facebook started charging $1000/hour to use, people would suddenly find it is in fact not really a necessity of life and would somehow find an alternate way to contact their families.

Why are you calling them, texting them, visiting them, or keeping in touch at all? Must be an unhealthy sense of FOMO!