The biggest problem with a simple architecture and often why someone would complexify it up, is as a protection mechanism so you don't get some performance review motivated yokel doing a drive by to add in a feature and look like a rock star because it was so damn easy. NSS, that was the next step. You see this in open-source as well. Someone builds a beautiful foundation, and Steve rolls up with a submarine pull request to slam that cherry on top.
A complex architecture ensures that you can adequately gate keep.
The next aspect is you have to relentlessly say no to feature requests that literally destroy the system to add some new feature, the pressure to smash it to bits and make it a no longer simple system is such a perverse incentive that unless you have support from on high, every simple system will decay into a total mess, then the finger-painters will have moved on to some other system to predate on.