When liberalism fails, people look for alternatives. Historically speaking, the lower classes move towards socialism, and the owning classes adopt fascism to protect their privileged position from socialists. Apart from some important exceptions, libertarian forms of socialism generally haven’t been able to prevail, while one-party states have built third-world countries into superpowers more than once, which makes for an appealing role-model, especially in countries where the system beforehand was a monarchist dictatorship or US puppet pretending to be a democracy.
I don’t know enough to say if it’s more insular or not, I don’t know how common it is to have the default sort as All, but we’re definitely worldly enough for other instances to have some users pushing stereotypes on us when we comment.
You do have some point about lemmy.ml having enough instances that you can get by with Local as default, but I assume most people would be subscribing to or exploring other instances too? I really don’t know.