They're not just hosting it - they bought it for $100 million
Even if Spotify wasn't effectively publishing the Joe Rogan Experience, I do think Spotify's employees have grounds to complain. Spotify has not built themselves as an open platform for free thought - they have built themselves as a curated music streaming service. Employees who do not want to support an open platform for free thought could be justifiably upset.
I'm just sick of open platforms in general being expected by external forces to curate their content like a publisher.
Not really. The expectation is that as a paying customer you’ll have access to the music you’re interested in. Their shtick has never been curation.