Playing devil's advocate here but some people may feel comfortable writing with a certain gendered individual, or even discussing certain ideas. The statement of "this isn't a dating site" is correct, but does broadening your horizons with who you talk to requires that you must be open to all individuals?

To give an example, in my characters I tend to play a female role. Probably 80-90% of my characters turn out female. On the odd occasion I will have an interest in playing a male role and the first priority I set is to find a female player with a decent idea for a story. This isn't for smut reasons or adult matchmaker, but a female player will most likely play a female role, which works out well for a M/F character pairing.

Generally speaking you will also find different gendered writers will write differently. Language, mannerisms, introduction of life experiences into the story; a male will typically lean towards adventures and action, whereas a female will learn more towards romance. 

Taking those two points into account, let's say I want to write a non action rp—maybe something with a little romance and less macho... I'd probably be on the lookout for a female writer. This isn't anything to do with sexism, misogyny, or even gender equality; it's about obtaining what I want and need to achieve a story that I want to write. If that so happens to mean that I have to restrict my preferences to a writers gender and it's going to improve the odds of finding a pairing that I'm happy with, then that's what I will do.