Search, Android, Chrome, YouTube, Maps, etc. are all staying under Google. The stuff that's going under other Alphabet subsidiaries is the stuff that's totally disconnected from Google's core businesses, like Calico, Life Sciences, etc.
> Sun is the loose cannon of the computer industry. Unable to see past their raging fear and loathing of Microsoft, they adopt strategies based on anger rather than self-interest. Sun's two strategies are (a) make software a commodity by promoting and developing free software (Star Office, Linux, Apache, Gnome, etc), and (b) make hardware a commodity by promoting Java, with its bytecode architecture and WORA. OK, Sun, pop quiz: when the music stops, where are you going to sit down? Without proprietary advantages in hardware or software, you're going to have to take the commodity price, which barely covers the cost of cheap factories in Guadalajara, not your cushy offices in Silicon Valley.
http://www.joelonsoftware.com/articles/StrategyLetterV.html
By keeping Google as one, presumably around search, Google has a shot at avoiding the same fate.