The problem is that humans have so far have a pretty poor track record at synthetically reproducing nature
This is it. Zealous scientists keep thinking they've replicated something exactly and then decades later find they didn't even know what they didn't know.
For example, when formula was invented, mothers were told it was better than breastmilk. But then they are still finding out all the time, subtle ways that breastmilk has useful stuff in it we didn't even know was there, and can't replicate.
Not least because breastmilk from one mother changes everyday, based on temperature, infection, even mood.
Another example is honey. There's all sorts of interesting compounds in honey that we haven't sequenced yet. And again honeybees will put different stuff in it depending on the weather or local threats etc.
If they can't make formula to be exactly the same as breastmilk, what hope have they of making artificial amniotic fluid that's exactly the same? Especially as it changes daily, based on other stuff going on?
It's hubris, thinking you can replicate this kind of thing. It's not Medicine like a hip replacement or a hearing aid. It's actual new life.