Female Friends in Fanfic

I occasionally see on fanficrants the lament at the lack of genfic, the popularity of character bashing the "Other Person" and the wondering of why, if a male character is being paired elsewhere, fanficcers can't just write the unwanted female as a friend and nothing but a friend.

I also read one of those fics where the "girlfriend" becomes the matchmaker for a slashy pairing and recall a few fics in my recent reading that have also had the line that the main character loves her "like a sister".

It has me wondering if "like a sister" is the easy way of defining a non-romantic friendship between two characters of opposing genders. Like, it's a bit too complicated to say something like "she's a friend but not in a romantic way!" and "like a friend" is the shorthand for that.

Just some idle thinking, brought to you by Non-Rinoa-Bashing Fics.