Yes, the new code might be all polished, nicer, easier to maintain, supports C++ in its latest version, and C99 ... but just doesn't work brilliantly on old platforms, sorry.
You have data to back this up? Debian/m68k is using gcc6 and they have built around 10k of packages now, as well as the kernel, glibc etc. using newer gcc (currently gcc-6.2 I think).