The problem is that "to let them run just the things on their computer they want to run" changes when they want it to run something new. They don't care about cloud backup for their data? One hard drive failure, and suddenly they do. And if you want to sell the same version of the OS to different people, you need the union of what everybody wants and what everybody is going to want later.

But there needs to be a way to turn something off that you don't want, and to not get nagged about it repeatedly thereafter. But for that to work, there has to be a clear, easily findable way to turn it back on later.