From my perspective as someone currently forming a startup co-op: It simply takes longer. You cannot go it alone and it requires a community effort. Democracy is harder than autocracy (which most companies are, by default). Bank loans and more require collateral from an individual, which a co-operative by design deflects against (so there's co-operative friendly lenders).

I'm hoping the trend goes in a different direction for tech companies and they see that there's an alternative - but the fundamentals of co-operatives won't (and shouldn't!) change.