It's a compiler problem and there is no money in compilers [1]. If someone made an intermediate representation for AI graphs and then wrote a compiler from that intermediate format into whatever backend was the deployment target then they might be able to charge money for support and bug fixes but that would be it. It's not the kind of business anyone wants to be in so there is no good intermediate format and compiler that is platform agnostic.
1: https://tinygrad.org/