When you buy a Mac Book you usually dish out around 1500 USD at the very least, where the cost of materials is at best 1/3 of that. You mostly pay for the design, the OS and the privilege.
You can get a PC with Windows 10 Home Edition for 400 USD or so. The implied price point for the OS is way lower.
The economic decision here (re ads) is to be able to make some money on the mass low-end market, while still being able to develop a decent OS.
Case in point: Microsoft Surface Book, which runs at about 2000 USD and is a product comparable to Apple’s has no ads.
Also, a $400 laptop is hardly comparable to a $1500 Apple laptop. I've had one of those, and the hardware really sucks, and stuff starts breaking within a year. It may have the same CPU, but the rest of the components are really crappy. If you want an closer comparison, compare high end laptops with the Apple laptops (Lenovo X- series, Dell XPS series, etc), which run at a much more similar price. If they're lower, it's because they have more competition than Apple does (Apple doesn't license its OS to competitors, so if you want their OS, you must buy their hardware).
MS shouldn't do phone home, OSX shouldn't do it, and I'm pretty sure my work CentOS doesn't do it. This should be the default, and you should have to opt in, preferably for some period, for it to happen.
For ads, this should be disabled by default, and the user should be compensated in some way for receiving ads on an OS they paid for. Also, these and Candy Crush seem to be re-enabled after some updates.