Hay wagon as a base for a tiny home?

I'm wondering if there are any clear and obvious reasons why hay wagons aren't used as the foundation for a tiny home?  I realize they can't be hauled down the highway, but they can be moved around.  With the extra set of wheels, it seems like they could be maneuvered into place better.  The floor height might require a few more stair steps to get into.  I see them ranging from 7' -8' wide x 16' to 22' long with prices for used ones often in the 3 digits.  I have a hunch they have plenty of load capacity.