I'm sorry this happened to you, and hope you have had time to process the feelings that this must throw up for you.
You're absolutely right that for any other organ that randomly didn't function as expected, there would be investigations, a body of research etc. However because it's "just" breastfeeding, and "just" women there's so little research.
Health professionals frequently have very little knowledge beyond the absolute basics, because training isn't seen as important. It's infuriating because the (cheap and easy) sloganeering "breast is best" messaging is seen as an appropriate substitute for real information and support that costs health systems money. While conveniently shifting responsibility for the outcomes onto the individual mother rather than the system surrounding her, and calling it choice.
We know that for around 0.5% of women, milk doesn't come in - sometimes there's a correlation with blood loss, trauma, retained placenta, breast hypoplasia. But sometimes those things don't prevent a good supply and we don't know why. It isn't always supply and demand. Obviously that is the case the vast majority of the time, but on a site for mums as big as this there will certainly be lots of women who share your experiences.
It's utterly inadequate, and leads to so many women internalising feelings of guilt and failure, when they could not have done anything differently, and have themselves been failed by this horrid system. Thankfully we have a nutritious, safe alternative food source for babies, and I'm sure your little one is thriving, but you are totally justified in in feeling angry, upset and grieving that the information you needed didn't exist.
Yet another area where capitalism and patriarchy make a perfect storm of stomping on women's choices.