Why is the downgraded driver's license C1M?

[OFaith]

When a driver's license is downgraded, it is mostly downgraded to C1 because currently, C1 can be used for life as long as physical conditions permit. However, it often becomes C1M because the driver's license includes the additional M-class vehicle type, and there is no further downgrade for the M-class, so it naturally remains attached. The C1M license can be considered a combination of the C1 and M licenses. The C1M license essentially adds the M-class vehicle type to the C1 driver's license. Among them, the C1 license covers small cars, while the M-class license covers wheeled self-propelled machinery. C1: Small cars, small automatic transmission vehicles, low-speed trucks, and three-wheeled vehicles; small and micro passenger vehicles, light and micro cargo vehicles; light, small, and micro special-purpose vehicles; small passenger vehicles with seating capacity of 9 or fewer people. M: Automobiles, tire cranes, road rollers, tractors, harvesters, and specialized construction machinery, etc.