Why does the SDLC suck so much?

Why does product development(software development) in organization, and even small teams, suck so much? In my going on 9 year career, I've noticed how unsatisfied almost everyone involved with software development is. From a software engineering point of view, it's frustrating how little product teams understand what it takes to keep the lights on and why they don't or can't explain why things are prioritized the way the are. From a product teams perspective, it's frustrating it takes so long to get this "simple feature" out the door, especially when we could have done it in a week 3 years ago.

All this to say, or I guess ask, what sucks the most about software development in organizations for you? This can be experiences at a startup, medium sized company or your time at large companies. I want to understand why this is so terrible for everyone involved.