Embedded DSLs (e.g. PyTorch) have been hugely successful in the field of machine learning, so I think there is a bit of nuance here that you're not considering.

I also take issue with the idea that Python is simple. Python's semantics are anything but. The biggest issue the language has, performance, is a consequence of these poorly thought out semantics. If the language was actually simple it would be a lot easier to build a faster implementation.