Frankly, it's probably mostly due to lack of participation on other messaging/social media platforms. WhatsApp or Skype etc. groups work fine if you have friends actively using them already, and on similar schedules/timezones. In that case, setting them up on a group chat wouldn't be an issue. However, unlike pure messaging platforms, Facebook works well because of the bulletin board format (Google+ works, just that few(er) people -- in my case no one -- are really using it, and depending on the circles, with quite a bit of spam and reposts). Depending on schedules -- and in my case multiple timezones -- it's quite difficult to find the occasion to have longer conversations with friends across the globe. When those conversations are ongoing on a bulletin board "everyone" uses however, it is easy to participate (or not). On messaging platforms the message threads are typically more conversation like, so if you're not on the chat while it's taking place in real time, you are less likely to scroll through hundreds of lines of text later just to get back on track.
I haven't used Facebook outside of the U.S. so not sure how ads, spam, fake news etc seep into people's feed around the world and if they are bothered by it. There are a few settings that allow you to filter some of the crap, but in my experience the filters were/are way insufficient. Of course, the best filter is not to participate on the platform at all
It's true, I can always pick up a phone and call a friend, or email, ask how they are doing. Now where did I put that mobile number? Oh that's right, I didn't have it in the first place because my only contact with that person was on Facebook. Damn it. So to answer my own question, yes, Facebook is relevant to me, but it's too annoying to use.
Boy, that all came off as quite a bit of whaaaa.
edit: To sum it all up: I'm lazy.