100% agree with you here, and yeah I'm definitely leaning a bit too conspiratorial about it. It's probably not actually intentional, and instead just a product of the larger dynamics.
A while ago I read some interesting economic analysis about why more co-ops hadn't popped up specifically in the gig worker space, since it seems to natural to cut out the platform rent that eg. Uber extracts as profit. I'm failing to recall the specific conclusions, but IIRC the authors seemed to feel that there were some structural obstacles preventing co-ops from growing in those space. Something something capex and unit costs. It's certainly an area I'd be interested to see further analysis in.
Also you sounds like you might get a kick out of mayfirst.coop (if you're not familiar with them already). It's not exactly what you're describing, but the spirit is there. I use them for my web-hosting needs and have been extremely satisfied.