why? I just don't get it.

I saw a poster in town today advertising for people to "egg share". This is basically when a woman who is undergoing IVF treatment donates some of her eggs to reduce the cost of the IVF treatment, so that other women can use these donor eggs in their own IVF attempts. I simply don't understand the point.
I know that I don't want to have kids myself, so maybe I am coming at this from a different angle but I don't understand the urge people have to spend thousands of pounds either of their own or NHS money to try and become pregnant. Surely if you cannot conceive and you want to be a parent then adopting a child makes you as much a mother or father as creating your own biological offspring? And if people don't think they would love an adopted child as much then maybe they are not emotionally mature enough to become parents anyway.
I know people feel some kind of compulsion to pass on their own genes, and for the most part I don't take an issue with this - each to their own and all that, even in cases where I might think it really would have been better if that person didn't reproduce. I do however have an issue with IVF treatment being available on the NHS at the expense of that taxpayer. I really feel that if you cannot afford the treatment then it shouldn't be the taxpayer that pays. Especially when you have the ridiculous situation where people that do not and will not work are entitled to free IVF, so that the child can be raised at the expense of the taxpayer. It baffles me. And of course there are all the issues around people who have paid into the system all their lives being denied life extending drugs due to cost when the same hospital offers free rounds of fertility treatment. It seems like something has gone wrong when it is deemed more important to create new life when there are so many kids already languishing in care homes, when there are people dying in pain because the drugs are deemed too costly but in the next ward thousands of pounds are being hurled at fertility treatments with a very low success rate.
But I found the concept of egg sharing the weirdest of all, alongside sperm donation. If the child you are carrying is not actually your own biological child or that of your partner then why go through all the pain and expense when you are basically adopting at a very early stage? Why not adopt one of the thousands of children in this country and abroad who are desperate for someone to call Mum or Dad?
Maybe I am missing the point entirely but to me this just does not make any sense.