Dwell time is the time between the order is finished and it reaching the customer who gives thumbs up or thumbs down ( order is wrong ).

It seems from the initial glance that dwell time is irrelevant because a kitchen can just go to the next order but that's not actually the case because without yes/no from a customer the kitchen can continue to make the same errors without adjusting. In the world of ghost kitchens dwell time is terrible because in reality the only feedback the kitchen gets is an asynchronous negative review that will be received a day or two later at best. That's the reason why pretty much all ghost kitchen based restaurants rapidly flame out.

Not them, but I imagine that it's because your fixed costs never stop — you can't just tell your staff to go home and not get paid until the next customer gets in.

Every hour you're open, money goes out. You need to have continuous sales to even have the opportunity to make ends meet. Even if you're losing money each hour but still making a few sales, you have some flexibility with tweaking your formula to reduce the losses or turn it into a net even. If you're just sitting idly, you're just burning money without anything to do about it.