Because the MNM is one of the most unique, versatile, and well made pieces of hardware you can get. And because it is so deep it’s it can take a person years to learn everything it can do, and many more years to actually use all of those features! A lot of people who own an MNM will say something like “this is the most amazing machine I’ve ever owned”.
THAT’S why you don’t see them sold second hand very much.