Why isn't IVF covered under insurance?

I was born with crooked tubes, have had 2 ectopic pregnancies and lost 2 baby's and 1 tube. I have one tube left which is crooked. Since I was born with a "deformity" and cannot get pregnant naturally, why do I have to pay $20,000 plus to get IVF or to even adopt?? I don't see the fairness of this delicate situation. I want to give my husband a family. Any advice from women with this same situation or from a medical doctor?