Here is why you miss the boat: You ASSUME that, if the parents had to choose between leaving the kids behind or moving somewhere else for a better job, all CP's would sacrifice the job and all NCP's would leave their kids behind.
You assume that all NCP's are like your NCP. But they aren't.
Try this: Let's take two parents who live near each other. BOTH of them are dedicated to staying involved in the daily lives of their children, no matter what. They both want to move, but neither of them wants to leave the kids behind. Which one has a chance of moving AND keeping the kids in their daily lives? The NCP is totally restricted from that. Even if they gave a 30-day notice, filed with the court and had a GREAT reason that they need to move, the NCP has no chance.
All an involved NCP can do is pray that the CP doesn't move away from them. Either that, or they have to hope for a judge who cares about kids. Otherwise the CP has all the power and all the freedom to move with or without the kids. The NCP may only move without their kids, which most obviously don't want to do, so they are stuck.
Are you beginning to understand yet?