> if the work were too sparse and wants more work, why not join interview loops or take classes/training, attend talks?

because it's never that easy. If you try to get work from somewhere else maybe your manager starts to think you're bored or not interested, you definitely can't just leave and go mountain biking because then you look even lazier. So at the end of the day in every gigantic organization a substantial amount of people sits around and does nothing, that's just how it goes.

it's not first world, it's just that in bug business you're just a salaryman.