None of what you ssid means writing compilers is hard: just that the first ones or techniques are hard to do. Once it's done, it's another building block that can be chained together to solve similar problems. Using a ML or LISP with right primitives makes that even easier. Designing the right language and implementing modularly makes that easier.

So, I'd say the industrial ones are as tough as they are because they support hard-to-compile languages with many dark corners while bring implemented in the same languages themselves. Make problem hard for yourself then it's hard. Make it easier then it's... still work but only a tiny fraction of what you alluded to.