Good question! It really depends on how well the machine is maintained. There will be normal wear and tear replacement of parts meaning hose, belt and brushes. Under normal care and use the machine itself could last up to 20 years before a motor replacement would be necessary.
There could be 2 reasons for belt breaking.
1. The bearing could be inserted wrong on one side not matching the other.
2. Brush washers are missing on the shaft of the brush causing extreme heat to transfer through the bearing and heating up the plastic mount for the bearing. This causes the brush to run untrue and cause the belt to jump off center.