I'm not sure this is exactly what you're going for, but I have an answer here:
When the dice are fairer than the DM.
As in, the DM asks for specifics on how you resolve a task, but always seems to "gochya" on those specifics. Yet when simply rolling, he let's the dice fall where they may.
I encountered this exact situation last Gen Con. Most of the games were great, but there was one, where the DM would ask for specifics on task resolution "describe how you check the door," "how do you inspect the staff lodged in the stone," etc. And when given anything would play gotcha (clearly he had specific solutions, but since we couldn't read his mind we never seemed to get them)
. I (and everyone else) resorted to just asking for checks. He allowed it, Things went much smoother.
So there you go.
Or it's just that some people like rolling dice because, as it says in the DMG under "The Role of Dice" and "Rolling With It", it gives people a feeling that anything is possible.
For me I use a mix depending on the situation, but different people play for different reasons.