I deleted my FB account several years ago and you'd be surprised how many actually find my email when they want to invite me for something.
If someone can't be bothered to send me an email I'm not too concerned about going to their party.
Of course, such apologies always come with the implicit "...but if you don't get on Facebook, it's going to keep happening." I actually started to create a Facebook account, but refused to continue past the point where it asked for my email account credentials in order to construct a friends list from my correspondents.
Yes, I'm aware that's optional and can be bypassed - but when the relationship starts out with a boundary test as blatant and extreme as that, I'm really not interested in hanging around to find out where my new abusive partner is going to decide to go from there.
So I still don't have a Facebook account. As a direct result of this, I also don't have a meaningful social life any more, which is a shame, because I rather enjoyed the one I did have. I'm hardly alone in this. Is it any wonder there are people who want to kill Facebook with a hatchet?
It's just not something people think about, and that worries the hell out of me. We've never before seen a world where a single, rather secretive corporation, which has already shown itself willing to experiment with its users' perceptions in order to better serve its own purposes, mediates practically every interpersonal relationship of a significant fraction of the species. When I was growing up, that would've been nothing but fodder for third-rate dystopian sf, and yet here we are.
And for spontaneous events (wanna hang out in the park this afternoon?), facebook group chat is still the common denominator, although that might change with facebook forcing people to install their messenger in order to being able to use it on mobile.