Opposite experience for me. I barely know anyone who uses FB marketplace, FB groups, or messenger. The only use case for Messenger is keeping in touch with "old people" who used it with me 10-15 years ago. That's like 2-3 people who are left and haven't moved off yet

In my experience, the FB ecosystem, other than Instagram and WhatsApp, is totally irrelevant to the younger generation.

If FB didn't own Instagram and WhatsApp I think it'd be dying in the next few years. These acquisitions are IMO what's keeping it relevant.