MATLAB, Mathematica, and Maple

Do any serious programmers use these? Or just mathematics and science students?

I keep hearing about programmers here using programming languages such as C, C++, Java, Python, etc. but no mention of these three. Why is it that serious programmers don't use mathematical programming languages?

Because they're not very marketable.

MATLAB is not a general purpose programming language. Its use is very specific for science and computational problems. It's in the best interest of a programmer to learn general purpose programming languages so that he will be marketable to more businesses. Likewise, it's better for scientists and mathematicians to learn MATLAB/Maple/FORTRAN as that makes them more marketable for science.