As a library worker I hear a fair few reading peccadilloes. For some reason the revelation that it was the ship-setting that was the problem amused me. Not sure why, possibly because it seems slightly random -though I appreciate that it isn't for you.
Often I find that people don't like a certain subgenre within a favoured genre. Like a fantasy-reader I know who only reads secondary world fantasy, because she find it difficult to suspend disbelief when reading fantasy set in our world.
A lot of crime fans will only read British novels, or at least they won't read American ones -though that's probably a stylistic difference.

Personally I find that certain types of romance don't work for me, I think I have a narrow/limited definition of what's romantic and it takes quite a bit for me to be invested in a fictional relationship. However most books I read aren't just about a relationship, so I can usually focus on other plot strands.