Why use a commercially supported C/C++ toolchain?

AdaCore recently extended its support of C and C++ toolchains and now supports not only native environments (such as Linux or Windows) but also cross ones such as VxWorks, embedded Linux, and even bare metal (C only at the time of this writing). In a world where most developers have access to a C/C++ toolchain that’s included with hardware or OS environments, this produces a question - what’s the added value of a commercially supported compiler for C and C++?