Answer
A perpetual motion machine violates the first and second laws of thermodynamics. These laws have enjoyed theoretical support and been confirmed by boatloads of experimental evidence, in every situation considered to date.
Though it is very very very remotely possible that these laws will be overturned by a new invention, the US Patent Office would rather not waste its time, and rejects claims of perpetual motion.
Physicists consider constructing a perpetual motion machine to be a fool's errand.