Hm, yeah, shouldn't Twitch also be on there then?

I think this vague term of 'use' isn't being very helpful here. Does that mean actively posting original content? Commenting? Liking? Sharing? Just scrolling/reading? Seems all those modes have a much different involvement, and likely quite different measures.

I don't use FB myself (in any mode), so this is second-hand... but my younger friends (< 30) use FB only as a necessary, lowest-common-denominator tool to keep in touch with less-close family/friends. It's low-effort ambient connection, not passionate interest or obsession. (I'm in a rural area with fairly low online/tech interest, which might affect things too.)