My dentist seen a black spot that is in the upper part of my gums. said it doesn't look cancerous but wants me to still have a biopsy. why is this?

Be sure what it is : Black spot in gum, especially if it is new finding should be biopsied, want to rule out potentially serious problems like melanoma. Probably a benign macule, but needs biopsy.

See the surgeon: It is hard to diagnose or make any comment without seeing the lesion. It is best to have an oral surgeon look at it and if necessary make a biopsy so you don't worry about it.

Rule out cancer: Never a good idea to take a chance. Oral cancer can be very successfully treated if caught early. Best to see the oral surgeon for examination and biopsy if needed.

Several choices: It might be an area of increased pigment like a freckle, amalgam stain from when a mercury filling was placed, or melanoma. Definitely would have ENT or oral surgeon look at it.