I also have a hunch that socket activation allows for more predictability around what a not-running/listening-for-activation service's port is doing at the sysc

I also have a hunch that socket activation allows for more predictability around what a not-running/listening-for-activation service's port is doing at the syscall/kernel level, which in turn makes power saving and/or sleep states a little more predictably efficient. Total guess, mind you.