This is something I find myself asking more and more almost every time I use a computer or mobile device. I have multiple cores here. Why is anything stuttering? Why are these processes taking so much memory up? Why is this web page pulling down 100MB of traffic? Why do I remember text console DOS apps being so much more responsive than today's click-then-wait UI apps? Before spinning hard drives dropped out of fashion, you could hear that thing grinding away, doing who knows what, while the computer was sitting there supposedly idle! What gives software developers the idea that they can just have their software just wake up and do things without the user commanding it?

Just a particularly egregious example: If there's one thing that nothing on the entire system should preempt, it's the mouse cursor. If I move the mouse, the cursor should move instantly. There is nothing more important that the computer should be doing. I thought this was like a basic, very well understood rule and a solved problem. Hell, I recall a long time ago things like mouse cursor drawing were driven off a hardware interrupt. On today's "modern" computers, if I have a lot of applications running in the background, the mouse cursor will stutter and lag, and text input will be buffered and show up N seconds after I type. Totally unacceptable, yet software continues to ship like this.

EDIT: Sorry, the rant kind of drifted off of the "nobody cares about bloat" problem and into the general "nobody cares about performance" problem.