I've always disliked gopath, not really sure why it exists?

I know they wanted somewhere to put the code to make the download tools easier, and I do really like go get, but per-project venturing of dependencies is just so much more sane. Perhaps it's because google has one huge mono-repo, it just seemed best to replicate that elsewhere too? I'm not even clear how this works inside google though if they have python projects and go projects, who gets to choose the folder structure where the code lives?