I went through the arduous process of deleting my Facebook account about 8 years ago. 2 years ago, I started doing freelance software development, and at some point almost every one of my clients has wanted me to implement a Facebook login. I could say no, but then I'm likely losing my livelihood. And in order to implement Facebook logins, you need a Facebook account (to administrate and view documentation).
My girlfriend cleans up estates, meaning that when someone dies, she helps the family of the deceased clean up the deceased's house. A lot of that involves selling their stuff, for which she splits the profits with the heirs. It used to be that Craigslist was the best place to sell stuff, but increasingly it's much harder to sell stuff on Craigslist, and easier to sell on Facebook marketplace. And again, to buy/sell there, you really need a Facebook account. She also does other odd jobs, and again, most of these are found through Facebook.
Maybe Facebook isn't necessary for the ways you benefit from the internet, but your experience isn't everyone's.