To OP:
I've shared your sentiment about the forum particularly the FS/FT traffic levels and how they've waned over the past fifteen years since I first joined the site. Not much to be done about it in my opinion, it's simply the shift in the computer industries and the rise and spread/infection of social media and related sites as well.
Unfortunately I live in a small town and even craigslist is no bueno because hardly anyone uses it. It makes it a much different site and experience than when I lived in a larger city with a University and about 8 times as many people.
These days when anyone I know makes a suggestion of where to try to buy, sell, or trade parts whether it be for PCs or cars, they usually are recommending reddit or (even worse) a facebook marketplace. I don't use facebook and won't simply so I can try to sell something there. I refuse to use ebay just on GP, so it leaves options limited.
Hardwareswap on reddit seems to have a decent amount of traffic, but the mods of the sub changed the requirements TWICE after I had first joined the sub, and the changing of rules on-the-fly like that kind of turned me off. They were changes that, in my opinion, were not very helpful, they seemed more elitist than anything.
Also had a bad trade experience from there, guy just wasted my time and shipping cost and I ended up taking the item back and just being out almost $50 in the end. It's definitely nothing like the AT FS/FT of old.