You're right, but that's kind of the point of suckless. To them, we should all be using software that is small, self-contained, and simple in implementation; both GCC and Clang are too complex in that case. C++ itself sucks to them, so g++ and clang++ don't need alternatives anyway.

Sometimes, it would mean separating what one piece of software does into many in order to replicate what that one complex thing does.

I don't subscribe to their philosophy, by the way. "Good" software which is elegant and easy to use is often very complex in implementation. That philosophy is basically the "worse is better" philosophy: https://www.dreamsongs.com/RiseOfWorseIsBetter.html