Because novice users have money to spend.
Money has nothing to do with it.
I'm certainly not a novice, and I love to hack the hell outta my stuff, but for my day to day computing outside of the fun stuff, simple works just fine.
Of course it does, but how is a standard OS not simple enough? As far as I can tell, it's as simple as can be: turn on the computer, it boots to the desktop, you double-click the icon for the web browser. Click the red button to close it, and press the power button to turn it off (it will shutdown for you).
A child can use an iPhone with no real instruction, try that with a laptop.
To do what, exactly?
My point is there will always be what we the readers of this forum use, the "old" style computer, but more and more the simple devices that do what we need quickly will prevail.
The one thing I will give you is that the simple OS is quicker to boot and is more appropriate for instant-on devices like the iPhone.