A lot of users are also from poorer countries that lack the means to create their own web infrastructure. Using Facebook to run your business account is easier, cheaper, and more reliable than most alternatives there. Phone carriers and ISP often also have “free”-data for certain social media platforms. You get 1GB+1GB for Facebook/IG/YT/Some Game. So you are stuck in this loop where everything reinforces itself to use Facebook.
I don’t think that the beacon works that way. The way I interpreted the comic the beacon has been active for the two years and still no help arrived.
Destroying it doesn’t really change anything, most likely it wasn’t working anyhow because otherwise you aren’t stranded for two years. It might just make it easier to accept rescue isn’t coming. And doing it voluntary because you prefer the lifestyle could be good moral boost.
But yes, if you are voluntary on an island you want means to contact help. What Masafumi Nagasaki did sounds pretty sweet sometimes. Living naked and alone on an island just getting groceries every few weeks for 30 years.