Why Don't Most Insurances Pay for Fertility Treatments???

I literally do not understand. Why aren't procedures like IUI and IVF covered by most insurances? While having children is of course a very personal choice, I feel like we should all have the right to make that choice. I think it's an integral part of the human experience that no one wanting children should be denied. If assisted reproductive technologies are MEDICALLY NECESSARY for some folks to have kids, then why isn't it covered in most medical insurance policies? Seems like many insurances will help cover diagnostic testing, but then if a problem impairing fertility is actually discovered, you're SOL. I'm still just on ovulation medication (Femara), but if, god forbid, I DO have to move on to IUI or IVF in the future, we'll probably have to choose between buying a house and having a baby... and that's not a decision I feel anyone should be faced with... I just don't get it, and I feel frustrated on behalf of everyone with fertility issues...