LOL!! this is great
(extensive discussion of engines and coding)
The term 'engine' is something of a misnomer, isn't it? It's more like... you have the VERY basic framework for a car. You have an engine, steering system, wheels, and maybe a transmission.
Everything else, from brakes to lights to the sound system and the car body, is on you.
Software complexity and interactions also factor into this. Even well-written code can have unexpected interactions when it's meshed to something else (this is what makes beta testers and QA employees cry a lot). To continue our car analogy, it's as if putting headlights in suddenly means your transmission becomes reversed.
And then you square and cube all these problems when you move to MMOs, since you have multiple players interacting in often unusual ways.
You know what I'm weirdly reminded of? The 'auteur' era in Hollywood. It seems like we're going through the exact same thing here.