Why would doc want a colposcopy if normal paps yearly and negative 16/18 hpv but only this year high hr hpv but negative 16/18?

The decision to pursue colposcopy depends on underlying risk for cancer. There are other high risk subtypes of HPV besides 16/18 that cause cancer. You did not mention what the cytology result of the pap smear was, but this may have played a role in your doctor's decision. Please talk with your doctor before the procedure to ensure all of your questions are answered before proceeding with it.