To answer your headline question the reason is that the two groups are independent. The people who voted to close on SO thought the question was a better fit for SF and we disagreed.
Some of the people voting to close your question on SO don't have accounts on SF and collectively they have <1k rep so obviously they have a good feel for what is topical here.
I'd be willing to bet that most of them didn't read much past the first sentence of your question either because you use server when you mean application and obviously all server related problems are for SF.
I have flagged your original question and asked that it is reviewed and reopened by an SO moderator.