We have too many different, interacting parts in most software systems these days to demand devs have pro-level expertise in every part they might have to deal

We have too many different, interacting parts in most software systems these days to demand devs have pro-level expertise in every part they might have to deal with. If you can simplify the code (without significant harm to functionality) so that only 10% of your potential devs wouldn't understand it very well instead of only 10% would understand it well, you have just increased the value of the code.