But rST is deeply linked to python: as far as I know the only existing implementation is in python, the touted "extensibility" is based on python, etc. Other languages don't seem to adopt rST because they don't have this deep relationship with it.
Markdown has a lot of implementations (with some fragmentation, granted) and is adopted by many diverse projects outside the python sphere.
Where I've automatically marshalled zig code into the elixir documentation (https://hexdocs.pm/zigler/beam.html#get_f32/2) and you can click the slash in the upper right of the function header to link to the code on Github.
As a bonus, check it out on mobile and compare it to this on mobile:
https://www.python.org/dev/peps/pep-0287/