Now info you search for online about cars comes from forums that haven’t had a post in the last year, yet in 2009 someone asked a great question about part compatibility.
We need a pirate effort to exfiltrate this data back into the public domain.
No, even that is terrible compared to forums – it doesn't get indexed by search engines!
This is a larger cultural issue. The general population finally got used to being on the Internet, and the Internet adapted to serve its needs and modes of thinking - which are predominantly social. Objective reality, information and access to it is of secondary importance (if even that) - what matters is socializing with friends and having experiences.
Unlike Facebook and Twitter, WhatsApp and Discord are the true social media - they work much like real-life interactions. So to join a topical group, or even know it exists, you literally have to know the right people. Don't have friends who are into something? Don't have friends? Tough luck. It's high school again, but the Internet is owned by jocks now.
I'm not sure what you mean by that in this context. Just like I have to be part of my local "nerdy" store to play MtG every Friday, I kinda have to be part of local MTB groups to know when they are riding. I could like you say, be a leader and organise my own rides I suppose? Is that what you mean? If so, then I'm sure you can see limitations to this approach.
Searching the forum archives is much worse with facebook, slack or discord than it ever was with even the jankiest phpbb forum or mailman list. Hell, before they grew it up, Yahoo! groups were better from that perspective. And a big part of what made forums for either tech or non-tech hobbies so nice was the ability to search and reference prior discussions.
I was actually hopeful that "login with facebook" and "login with discord" would bring those more search-friendly alternatives back a little bit, but so far I haven't seen it.
As a result it's far better than "omnisearch" options on social media that only sometimes surfaces what you were looking for.