Happened to me recently during a call. Perhaps they could have phrased it better, like “why are you open to opportunities” (which sounds quite dumb too tbh)
They want to understand what you didn’t like your past job and role as well as understand if you can have an adult conversation and not blow up former colleagues for example. Not everyone starts the interview process from the same point and interviewers likely don’t have full context.
I regularly get interviews from people with little social or communication skills even in the context of a small team.
It doesn’t take many times being on the hiring side of the table or talking with someone who is, to hear the horror stories of why the stupid questions get asked.
Lol… (sorry, it’s funny but also makes sense it can suck being on the other side).
To me the question is flabbergasting - I genuinely have no answer. It’s like asking “why do you want the sun to rise in the morning?”.