Hi I was told I had a polyp that had to be removed by having a D&C, why?

I have a lot of pain all-ways, and for years, Ive had a colonoscopy done and had polyps that was their, I'm still all-ways in pain in my stomach only, then I went to the woman's health clinic and had test done, ultrasound was done blood work was done and a byopsy was done, now their saying that theirs a polyp in my woman area that should be removed, why do these keep growing? and why does it need to be removed. Thank you