Mostly because I am familiar with Python and I don't want to learn the syntax for the advanced expressions I will seldom use. c() s() etc instead of cos() sin() is not too bad, but if I have to do a specific rounding/truncation/modulo, I probably know how to do it in Python and I definitely don't know how to do it in bc syntax.
Of course a similar shortcut can be defined for your language of choice, if that's JavaScript/Ruby/R/... then you probably want to use that.
