Why do woman with pcos have bad egg quality? is it something we can do to improve the quality of the eggs?

Sometimes yes: Women with pcos usually have plenty of eggs present in the ovaries: they just don't mature and ovulate on a regular basis. If overweight, losing weight can improve ovulation. Some women find that myo-inositol supplements (chiral-balance or pregnitude are two brands available) may improve ovulation as well. Be sure your thyroid function has been tested also.

The don't: The problem is not the quality of the eggs - it is the lack of ovulation. The ovary must release an egg each cycle for there to be an opportunity to conceive - with pcos the ovulation is infrequent or absent and there is less likelihood of conceiving. The eggs are still just as good.