Speaking as a machine learning and neuroscience researcher, how thoroughly have you investigated the matter to claim this? I would definitely not say that we have "no" understanding of the subject. We have a number of predominant paradigms and competing theories regarding the matter.
We do have some understanding, even if it is somewhat limited.
Anyway, that there are many competing theories about intelligence can mean one of three things: either they're all mostly wrong, or some of them are mostly right, or all of them are a little right. Which one do you think is the case, regarding the theories that you have in mind? And what are those?
Me being a dual trainee in both fields, well, I'm working on it.