Yeah I could imagine that being underground 90% of the time would be depressing. At least for bus or streetcar drivers there are things to see, activity & life on the streets.
A friend of mine drives the subway and used to drive streetcars, and actually likes streetcars. But he doesn't miss "things to see, activity & life on the streets" which for a streetcar driver, generally consist of traffic congestion, cars driving aggressively, cutting off the streetcar and then stopping in front of you to make a left turn, bad weather problems such as parked cars blocking tracks in the winter, snow and slush-covered switches that you can't see if they've changed properly, aggressive and/or foul-mouthed passengers, getting out to do manual switches when they short-turn you, and then dealing with more aggressive/foul-mouthed passengers when you're in a huge gap after you get short-turned, plus in the summer, hot and uncomfortable streetcars. At least with the Flexity cars, they won't have to interact directly with passengers, and there will be air-conditioning, but the rest of it will be the same.
In any case, he loves driving the subway. There are plenty of delays and the risk of a jumper, but overall, he is way more satisfied with working in the subway and he has no plans to go back to streetcars any time soon, even to train on the Flexity cars.
With respect the box under the platform, I believe kotsy is correct. Bodies are removed immediately and nothing moves until all of the person is accounted for. Morbid for sure, but it wouldn't be any other way.