It's been available in pieces for years through various publications. There was a time when the World of Greyhawk was only available via mentions in modules and the core books and people played there. And there was a whole lot of anticipation for the Greyhawk folio when it came out as a result. (I know, because I was one of the people excited to lay hands on it.)
I was on the NG patreon, so I was getting access to the PDFs, and have the wormskin zines from before that. But it just strikes me as so odd to purchase a retroclone just to play one singular setting that hasn't even fully come out (and apparently these people exist, because they were mad about the dolmenwood OSE house rules). The whole point of OSE is that it enables rough compatibility with TSR-era modules plus a large share of OSR-modules.
The OSR scene has always had a big cult of personality component, even after the G+ era. Gavin is the current big dog in that space and has so far stayed blessedly unproblematic, as far as I know.
We do enjoy our auteurs, it's true. It's always nice when they're not jerks.
