Because it takes capital to start a business. People with capital like to retain control over their capital, so they don’t start cooperatives.

Coops don’t have the same incentive structure as external-investor-beholden corporations, so they don’t pursue “growth at all costs”, but rather survival at all costs (job preservation), and then growth where appropriate (pie expansion).

It’s kind of like the trade off between authoritarian regimes and democratic regimes. One is fast but flimsy, the other is slow but robust.

Banks dont want to lend money to them as often/much/favorably, coops usually don’t want investment.

To start a business you need capital, if you have enough on your own, you do not need a coop, much more difficult to convince a group of people to risk together unless they’ve all had previous experience with one another.

Why would Banks shy away if they are more productive and have better margins?

Banks calculate risk by looking at data, and there is far less of it for coops. And they are often irrational actors.

Don’t discount that they’re also seen as a threat to the status quo

They aren't a threat , which force is stopping coops from starting exactly?

No they are not, there are so few co-ops that nobody cares about them. No politician campaigns promising to destroy co-ops, not even Trump, because there is no reason to.

I doubt the demographics of coop participation are even partisan. Urban organic food coops probably skew left, but all those rural infrastructure coops, fuel/etc service for farmers, probably skew right. Attacking coops wouldn't win you votes with many people on either side.