To add one more detail to this, in writing Emacs, RMS resisted the trend towards lexical scope, and as a result Emacs got stuck with dynamic scope. Furthermore

To add one more detail to this, in writing Emacs, RMS resisted the trend towards lexical scope, and as a result Emacs got stuck with dynamic scope. Furthermore RMS failed to create a kernel because he believed the micro-kernel hype. But micro-kernels are hard to debug for all of the reasons that micro-services are challenging to scale and debug today if you have failed to create a good toolchain around them. And the result is that by the time that the GNU Hurd was available, most were using Linux and most of the rest were using Free BSD. (One does wonder, however, what would have happened had RMS himself not been crippled by tendonitis. Could he have finished in time for his kernel to be relevant?)