I did a lot of work with transputers and occam in the 1980s and wrote an OS for a machine that used them. The exposure to the CSP way of thinking was a blessing. occam-2 on the other hand was a little too primitive.
I remember when Inmos marketing came up with "We wanted to make occam the FORTRAN of parallel processing". My response was "You have." (a reference to occam-2 having only static arrays and no concept of a record/struct)
They had a functioning compiler and decided to concentrate on other areas and it's not too uncommon for a languages's compiler to NOT be written in that language. Afterall Rust relies on the non-Rust LLVM.