They want to get the monitors to run so they can make sure it’s fixed. If they let it go, not knowing it’s fixed, they risk having an unhappy customer. It’s not rocket science.There's a reason "courtesy" / loaner car is given to customer by a shop / dealer, but a customer giving their car to a shop to just "drive around" simply doesn't sound right... (what incentive would the shop have to return the vehicle to owner asap?)
it’s also sometimes necessary with intermittent problems to try to get the problem to show up. I don’t think most techs love just going out and driving around. None that I know think it’s the best use of their time.