Eh, most developers I know are lazy and won't even measure the performance of the thing they're building if it's "good enough". I can't remember the last time any of us fired up a profiler. Optimization is generally hard and un-fun.

On the other hand, developers love to build shiny new stuff more than they like using things that are already there. The "Optimize" part you're talking about is more "reinvent the wheel" in my experience.

Figuring out how to use X new library isn't fun. Building this cool thing that does the same thing but better is a lot of fun! That's why things get overengineered and built for "scale", which is probably mostly what you'r referring to. Instead of taking something off the shelf that would work fine some developers are compelled to build something that can handle the entire traffic of the internet. They don't achieve this by optimizing what's there, they do it by building an enormously complex system for no reason :)