Hello, I Have A Cyst On My Ovary That I

Hello, I have a cyst on my ovary that I believe is about 2-3cm. Which is not big and not causing me any trouble except that it has been there for a long time and at 45 I am in the peri menopause stage probably close to menopause. I am waiting on operation to have it removed via laparoscopy as the surgeon thinks that is the best option. It has been there for probably 10 years that I know of. The last 12 months or so there have been a few scans, with it getting as big as 4.5cm (I had a mirena in at that time) and has been getting smaller down to @2.5cm. My question is, why would I have this cyst that has been there for such a long time and won't go away?