One thing I've learned about social interaction is that people generally LOVE talking about themselves. So that's a skill that I've learned about making small talk adnd friends is that you generally can't go wrong asking people to talk about themselves. It's a subject that you know the other prison will be interested in also know lots about. I have actually become good at creating small talk and making new friends in this way - people can reveal as much or little as they want, but either way you are on the path to being friends. So I think these people expect you to like to talk about yourself and a are trying to be friends, or at least be friendly. They are trying to make pleasant conversation that you would enjoy. Some people are just trying to be nosy, but mostly, your example questions seem honest and innocent.
If you'd like to maybe make friends, or just practice social skills, I would say just answer somewhat briefly but honestly and then return the question.
If you just want them to bug off, then you can give a short answer like "oh, no real reason" or "I just wanted a change" or it's a long story". The person will likely back off because they'll know you arent interested in talking... however, answering honestly and letting the conversation keep going is a better idea I think! In talking about your lives, You might find that you have something in common!