As someone who does a lot of local organizing, I really don't think getting SSO set up in this level of organization is a thing that happens enough to impact pricing decisions at Atlassian. Even if SSO was completely free everywhere, most of these kinds of places would still just be using a single shared account with a shared password.

Stuff costs money! That's really all there is to the analysis. You can demand that companies not price-segregate customers, but then all you're really saying is that there's no account that the local PTA can afford, because you're demanding that vendors raise prices on the low end and and drop them for customers like Apple and Ford.