bearing and shaft in 47 inch snow blower are ruined - does anyone know why?

I have a 322 JD lawn and garden tractor with a 47 inch 2 stage snowblower (front mount). The blower is 20 plus years old and all was ok until last winter. When blowing the driveway there was a howling noise. The shaft coming from the pulley has 2 bearings in a block which goes to the driveshaft that goes to the gearbox. The bearings are cutting into the shaft and ruining both the bearings and the shaft. I replaced the shaft and bearings 3 times since then and after blowing the driveway again today the same thing has happened.

Does anyone know what would be causing this to happen?