The reason why I don't use it is because I never have been in a situation where it was required. Granted, when I took an AutoCAD class, AutoLISP was mentioned, but we never used it. I do a lot of under-the-hood stuff so I rarely venture out of C these days. C++ is just object oriented C when you get right down to it. I've only used PHP, JavaScript, and VBScript in the context of web development. For Microsoft platforms, Visual Basic, Visual C#, and Visual C++ are the staples that I use there. I have looked at Python. It looks interesting as a functional language, but you don't get into the detail work that is standard fare for C/C++ and even C# to some extent. I have never really used Ruby.
So I guess it comes down to the fact that people use what they know, what they are comfortable with, right tool for the job, etc.... I would imagine it's the same issue why we don't see LOGO, ADA, or Forth in common use (I know that Forth is used as the FreeBSD 3rd stage bootloader when booting the system). Fortran and COBOL are still used in their respective arenas (scientific and business apps), but that is going by the wayside as well. Although Java is still a relatively strong contender, most other non-web languages are becoming victims of the C++/Python bandwagon.