There has to be some of it out there now, but it'll be scattered around blogs and forums and random social media sites, and finding examples is more a matter of luck than anything else. The OSR community has preserved some D&D camapigns that way, but digging up "war stories" for (say) early Traveller is a lot harder, and when it comes to less popular games gods help you. For ex, I'd kind of like to know what people actually did with some of the FGU games back in the day, but if there's a Space Opera or Bushido campaign memoir out there I've never seen it. I was lucky enough to randomly stumble on a titanic V&V diary that spanned decades and hundreds of sessions from multiple groups one GM ran - and then lost the url and I've never found it since.