Get used to it. That's how you're going to get paid by the time you're done with residency.
To answer your bigger question, the problem with something vague like "personal issues" is that it could be something legitimate but not particularly worrisome in the long run, like the marital issues you described, or the death/illness of a close family member (and by this I don't mean Grandma or your aunt...parents, sibs, spouse, kids, that's all that counts), or it could be a significant personal physical or mental illness, in which case it may have long-term repercussions/impact on your training, or, it could be (as happened in my residency program after I left but while I was still a fellow at the institution) that your cat died and you couldn't pull it together to go to work for 6 months (no s*&t...true story).
In the first group above, PDs are likely to say "bummer, good job taking care of what you needed to do and pulling through". For the second group, they're going to have legitimate questions about your ability to do the job that you will hopefully be able to answer. And for the 3rd group...no...just no. So, when you come for an interview and I ask, "tell me how you handled the issues that led to your LOA and how that will make you a better physician?", if you answer "I had personal problems and I fixed them" I'm going to assume that you're either one overnight shift in the ICU away from going full nutty on me or your cat died 6 different times during med school.
That's why you answer the question.