Very true. I think it can go the other way as well. I know I would be interested in writing a much broader range of stories than I tend to read, which does sound weird, but I don't think I approach reading fanfic in the same way as writing. I like the more limited scope of shipper fic, where you can appreciate very subtle differences in approach and small variances on common tropes and the whole thing is a close-knit conversation with people who have all read many of the same stories. When it comes to writing, I'm much more with you - bits of back story, peripheral characters, different motivations, possible futures. And it's not that I don't like reading those too, exactly, but I read them as I would read anything else, a book say, whereas OTP stories are in a separate category. For fic in general, it's competing with my whole To Be Read pile, and there's the difficulty of wading through piles of stories to find good authors,* whereas for shipper fic, not only is it a smaller pool of writers, so I quickly get a better idea of who I particularly like or dislike, but I tend to like more of it, because there is more to be interested in than just the quality of the writing. I don't mean that I'm happy to put up with bad writing if I like the pairing so much as that even an average fic is taking part in the communal conversation, so I can appreciate it on that level separately from appreciating its quality.

* I do tend to read everything by writers I know I like, except for stories that are clearly best appreciated as part of a shipper community discourse I don't take part in.