Not sure I agree, I have no social media account and have no desire to ever get one. Whilst I accept I am in the minority I am sure I am not the only one.
Social media's strength is in its convenience and its weakness is its content transience. In comparison, I believe a forums strength is its persistent quality content and volume of visitors. This is made more than obvious by the the amount of technical questions, build threads et cetera. Trying to find a "thread" in one of the plethora of social media groups will be a nightmare because they control the order and visibility of the content. One day it will be there and the next you can't find it . So while social media is constantly hosing out new noise to keep its users attention, forums enjoy strong search engine results and a steady stream of new blood.
There aren't a glut of daily for sale threads because it's so much easier to post a picture and a price on social media via a phone. In my opinion people would also rather rip someone off via social media where they can delete a for sale advert rather than on an open forum where it can be seen for months and years to come and where there is very little protection or chance of a comeback.
You only have to look through the for sale threads on here to see the ridiculous prices some people are asking for old technology, secondhand and OEM parts. Also this new trend of labelling parts as "rare" is now being used as another way of increasing their value. This behaviour of Supra tax is accepted on social media, not so much on a forum.
You still get the idiots trying it on with pricing who manage to sell parts to members with more money than sense or members who are so desperate to own a "true" OEM part they will pay way over the odds but thankfully most of these rip off merchants have moved away from here now. Unfortunately they do rear their heads from time to time but mostly find out what a part is worth only to advertise it via social media for a lot more than the price given.
This forum isn't dead, far from it.