When you start using new features you break backwards compilability. For C11 that means distros as new as Ubuntu 10.04 (which I still use as my main desktop) and the like are going to have problems compiling (GCC it ships with only supports parts, as in C1X). This will also apply to older embedded systems where a tiny client would be useful.

In the past a compiler and ecosystem would last a decade before it couldn't compile something. These days changes are coming out, and being used, every 3 years. It's future shock and the major cause of container usage on the desktop and in academia. Sticking with a well established older standard means everyone can avoid the massive increase in complexity and problems that containers bring.