I read and write only in English so it makes sense to me that the community I started and continue to run is in English. If people want to post bilingual content they can do so elsewhere, there's many communities that will accept it, although I notice quite a few are making English only as a rule these days.
I know some people get annoyed about it but it's not going away, the English only rule, I mean.
Thanks for your question. I'm not sure if you were hoping for some other reason, but the reason is so simple....I only speak English.