It's not clear what you mean by "never widely adopted". With the exception of MSVC, are there any mainstream C compilers that don't try to follow the C99 spec?
Sorry that I was unclear. I always use a C99 supporting (gcc/clang) compiler for my own C projects.
However, the problem is that because MS doesn't adopt it, a lot of companies and projects still have coding standards that forbid the use of C99 constructs. This because of the (percieved) need to compile for Windows with MSVC some day. So MS not adopting C99 is a problem for adoption, even though most compilers support it fine.
