I think it’s just because most players tend to be good at micro, but not so much macro.
Having a set “build” takes the macro thought of your item choice out of the equation so they can focus on their micro. The thing is though, you can easily make up for subpar micro with good macro. Picking the best items for a given situation, even if they aren’t necessarily “meta” is incredibly important and something most players just don’t feel like mastering.
In broad strokes, yeah. I’d even consider older, more traditional forms like forums and IRC/BBS to be proto forms of social media. As long as the internet exists there will be social media, what form it takes is malleable depending on the desires of the userbase at hand.