I haven't got time right now, but I'm going to chew on this for a while and try to give you a more reasoned reply.
To start with, though:
Imagine teaching "Little Women" to fifty teenaged boys.
Sometimes it's just difficult to invest in a story in which People Like You don't appear at all. Gender is not like race--I can read Chinua Achebe and not feel marginalized by the relative lack of white people in the story, for geographical and other reasons. But gender transcends geography: there are female hobbits, Elves, and Dwarves, to say nothing of female PEOPLE all over the world. A story that doesn't include any is making a strong statement.
A story like The Hobbit, which effectively ignores half the population of the world, can be hard to relate to despite its (many) other virtues.
Note to everyone: I AM NOT SAYING TOLKIEN WAS A SEXIST; merely that there aren't a lot of women in The Hobbit. (Are there any at all? I don't have my copy here at the office, and as it's my least favorite of Tolkien's works it's been a while since I read it).
Perhaps your female students are finding it difficult to engage with stories that just aren't about them, period, full stop. Please note, though, that this is not something you necessarily need to remedy in regard to the works in question. They need to be able to stretch their minds and get into these less-readily-accessible (to them) stories--that's what learning is about, isn't it?. In addition, the literary canon (and genre fiction, and movies, and theatre) is chock-full of stories that Just Aren't About Women. If they're ever going to read, watch, or listen to a story, they've got to get used to it.
I'll note that there are also a lot of stories that Just Aren't About Men, but I've found that men are much better able simply to avoid these (sometimes by relegating them to some kind of secondary-genre status...but that's a whole other discussion, not even remotely Tolkien-related, so I'll just screw the top back on that can of worms if I may), while not depriving themselves of literature, film, etc.
I haven't really addressed the question of how to approach The Hobbit, but I hope I've shed some light on what they may be thinking.
Then again, maybe they jsut didn't do the reading and are looking for an easy way out by claiming to be oppressed. (I wasn't this cynical before I had students of my own.
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