What year was this?
Except you're taking about before 2011/2012, I see no reason why one should go to a social platforms like Facebook to transact with total strangers, with the high risk of getting scammed and zero protection against it happening
Due to various reasons, social media like facebook was one of most popular medium for Bangladeshi crypto user to exchange their crypto into fiat. Some p2p used to ask for KYC which most of the people didn't like or avoided. I used to be a dealer back in the days when Binance didn't bring P2P. I had a lot of connections on facebook and telegram who used to buy/sell crypto to/from me on a regular basis. But now, people are using Binance though it's too asking KYC.