Squeezing that last mips out of the machine has taken precedence to structurally elegant but CPU hungry architectures.
However, my work area is resiliency and recovery so my “pain point” is the outage. This often comes device drivers in a monolithic kernel, this tends to take out the whole OS. A more compartmentalized OS (Minix3) allows a driver to be restarted without taking down the whole OS.
Just my view of the world.