As much as I hate to see the monorail go, I will say that they'd otherwise be sitting in a junk yard, those models are all being replaced with newer ones soon (AFAIK could be wrong), so I guess we can look at it as one last time for the old monorail to give people joy.
EDIT: I researched this. That's a Mk. IV Disney World Monorail, that when retired was bought for use by the city of Las Vegas. After years of use, Las Vegas started to use newer monorails an left the two Disney ones they own out in the elements for a few years. Monster jam seems to have bought this one as one last hurrah for it. seems like it had a great life.