Or more people need to learn German? The community is already there, obviously — if others want to join, that's how they do it.
But in the case of a larger online community where German is used by default, you'd be unlikely to get everyone to switch to English just by posting in bad German. After all, you might just as well be a Kazakh whose English is even worse, and as just another anonymous newcomer, there's no reason to accommodate you in particular.