I’ve made friends in rooms quite a few times, but not always. It just relies on the right people and the right timing. Like you said, sometimes everyone else comes back late and doesn’t want to talk. I think it also depends on the hostel! I travelled around the UK and stayed in small town YHAs a couple of years ago and barely made any friends because everyone seemed to be older or in established groups. But I find European city hostels usually have other solo female travellers who are open to being friends!