Cython is dependent on CPython. Cython outputs Python extension modules, which can only be used when imported into a standard CPython environment, and which interoperate cleanly with the rest of the Python ecosystem.
Mojo explicitly does the opposite, allowing Mojo to use Python but requiring Mojo to be in control, while making it hard/impossible for code written in Mojo to benefit code written in Python:
> Our long-term goal is to make Mojo a superset of Python (that is, to make Mojo compatible with existing Python programs). […] Mojo lets you import Python modules, call Python functions and interact with Python objects from Mojo code. […]
> As shown above, you can call out to Python modules from Mojo. However, there's currently no way to do the reverse—import Mojo modules from Python or call Mojo functions from Python. […]
> This pattern doesn't work because you can't pass Mojo callbacks to a Python module.
> Since Python can't call back into Mojo, one alternative is to have the Mojo application drive the event loop and poll for updates.
No comment on whether this should be viewed as an attack.
https://docs.modular.com/mojo/manual/python/