It can be rude. I've seen it where the significant others are put into the fic only to be trashed and written out in favour of another "one true love". However, most GOOD writers simply don't include them and choose not to address the issue. Tumblr's sports fandom just really seems to take this premature leap towards the conclusion that people who write fic or anything like that are unable to discern fantasy from reality. Which maybe true of some people, but not all. Fanfics are written because they're fun and they're not all slash. And if I want to post a fanfic where James Reimer and Jonas Gustavsson pilot a jaeger together in both their player tags I WILL DO SO, because fandom is large and AO3 has a growing number of hockey fics and WE HAVE TUMBLR. Fandom and its practices predate this website, and the number of younger people who simply do not know how to fandom (hint: FANDOM IS WHATEVER YOU CHOOSE TO DO AS A FAN) is baffling.