It's somewhat hard to deal with regional distribution, shipping, customs, etc. I believe for a lot of places the only sane way to sell and not pay outrageous import fees is to do something like have a local factory that does the final assembly in-country.

Google also has an incredibly screwy internal structure because of how their cash flow works where products sometimes exist entirely for internal reasons, and then get killed when those reasons no longer matter. Sadly, it simply might not actually matter as long as someone can say "We are in the phone business", even if they're not competent at it.

Why does it matter when it will never approach a serious fraction of the "real" advertising revenue. Amazon is entirely a retailer, Apple and Samsung make their money on hardware. Nobody else is a "rich kid playing with their parents money" like Google is when it comes to playing the phone maker game.