(Of course if you want to liquidate to non-trivial amount of money, you're probably not interested in speculation)
If you like your job, your cost looks very different from doing an equally demanding job you hate. The emotional cost is real and can have long-term effects on your health.
Plus of course clicking stuff on your computer is something you can do in your time wherever you are as long as you have an Internet connection. Working for 1-2 hours at a gas station (or McDonald's or whatever) requires a fixed schedule and commuting, not to mention that you'd likely need to agree to a minimum number of working hours and are unable to just skip it whenever you want.
"Why don't you do this other form of unskilled labor for minimum wage instead" is a legitimate question when the current alternative is time consuming and they're struggling to make ends meet. Not so much when it's something they do for fun every now and then while already holding a job that pays above minimum wage.
the thing to remember here is that money launderers are looking to push a lot of volume. they care about the volume of clean money they can get, even if that means negative margins (you are "paying" for the service). i'm guessing market making in crates is not a very high volume kind of service but I might be wrong!