This might be cultural, but where I live it's not really organic for friends to ask "how are you doing" without a lead-up. It's only done with people you see rarely, as a way to start catching up. In all my friendships the person who has troubles is the one to start the discussion about it. Especially with family related stuff, people can feel awkward about asking "so hey is your mum still being a fuckpuddle?"

There's also the chance that you're talking about your family problems so much that it's making them uncomfortable or burdened. Cold as it may sound, it does get tiring if a person talks about a hardship, legitimate as it might be, repeatedly and exclusively.

If you feel this isn't a case of you bringing up your problems constantly and are contributing to the conversation on a regular basis on other topics too, then your friends may just not know how to respond beyond "damn that sucks." It's possible they don't care and are bad friends, and to gauge this I suggest you talk to them about you feeling like they're being avoidant when you need support.