General list of Possible reasons for low/none GPU usage in Premiere:
1) GPU acceleration is turned off in project settings
2) There is no GPU accelerated effects on the timeline, or their processing time is minuscule.
3) bug in the latest GPU driver. Try to roll back to older version(s), also disable drivers auto-update in Win10. Make sure you are using 'Studio' driver, not Game ready one
4) GPU driver is too old, update manually from a vendor site (Windows update won't help). Use 'clean' install option. Again, use the 'studio' one and say no to auto-update 5) Your GPU is not supported anymore