What's really hurt Craigslist is all the scammers. You can't post anything of value on there without some scammer responding and telling you they're going to send you a cashier's check and have a personal assistant pick it up.
You don't have this problem at all on Facebook AFAICT. When someone responds to your ad on Facebook Marketplace, it's a real person who actually wants to buy your old junk.
In short, the formats of the sites make all the difference. CL was created to preserve anonymity and not be a centralized social network, but that feature is also its undoing because it facilitates scamming.
IME, Facebook Marketplace is far from free of scams and stolen merchandise. That's why some people call it Fencebook.
Thats not a new problem though, is it? I dare you to buy used car parts on ebay.
Craigslist was tainted by the unsavory element of prostitution and stolen goods and isn’t a resource that I seek out. Facebook marketplaces seem like what eBay was in the 90s.