>Have you ever tried maintaining that kind of code base?

I've never tried to maintain a code base written by non-CS people. In what context have you seen code by non-CS scientists?

>Having seen plenty of code written by non-CS engineers and scientists

There is a trade off between domain knowledge and programming style. Is it better to teach a BSCS 2 years of chemistry to work on your molecular modeling library, or hire somebody with chemistry experience who writes less maintainable code? Coding has become easier over the last 20 years, but the domain-specific knowledge has become harder. This trend favors the chemist over the BSCS.