I think it’s more that we know it (or some equivalent) can definitely work but that we don’t know the exact design this there is an expensive and time consuming

I think it’s more that we know it (or some equivalent) can definitely work but that we don’t know the exact design this there is an expensive and time consuming process of iteration which was not deemed worth it by those with the know how and capital to build such a thing. Mostly because those are the very people who were profiting off of the existing system.