I mostly understand asking about previous jobs, it's good to know what type of experience a candidate has, but why the hell do they need to know WHY you weren't working at a certain point in time?
I have a few gaps myself, I didn't start work until I finished uni so I have to explain to a complete stranger and justify why I decided not to work until I needed to. Then I had to quit my last job on the spot because my ex started abusing me and I had to move back to my home town where I couldn't commute to work (and wouldn't, not worth an hour and a half on the bus for minimum wage retail) and I've had no job for a while because it's dead here. Why's that anyone's business? What do I even say??
I know 90% of the stuff they ask doesn't matter, but genuinely why do they demand an explanation on some applications? What you gonna do, not hire this guy as punishment for him not having a job before? He's literally here now trying to get one!