Why are ex wives so bitter towards the new girlfriends and wives of their ex?

I split with my husband 7 years ago, we both moved on and remarried, i have never or ever be jealous of his new wife, i am more than happy with my husband, so no need for any bitterness at all, even though it was me that asked for the divorce. There are alot of bunny boilers around, obviously not happy with their own life that they have to attempt to destroy the ex. Sad really.