Why is dydrogesterone included with oestradiol in Femoston for women with an intact uterus?

Dydrogesterone is included with oestradiol in Femoston because unopposed oestrogens stimulate endometrial growth and increase endometrial hyperplasia and cancer risk, while adding a progestogen greatly reduces oestrogen-induced endometrial hyperplasia risk in women with an intact uterus.