Here is the difference:
DRIVER Match the driver name of the event device. Only set this key for devices which are bound to a driver at the time the event is generated.
DRIVERS Search the devpath upwards for a matching device driver name.
https://www.freedesktop.org/software/systemd/man/udev.html
I assume the device is not always bound to the driver when the event is generated.
Here is the difference:
DRIVER
Match the driver name of the event device. Only set this key for devices which are bound to a driver at the time the event is generated.
DRIVERS
Search the devpath upwards for a matching device driver name.
https:/ /www.freedeskto p.org/software/ systemd/ man/udev. html
I assume the device is not always bound to the driver when the event is generated.