[andrewwharton]

I'm skeptical that Google divides its revenue and investment up in this way and that more search ad revenue allows Google to invest more in search.

I'm sure that Google is already investing the amount they need to in search to make it as profitable as possible.

It seems that more search ad revenue allows Google to bank roll the rest of the Google/Alphabet behemoth on projects unrelated to search, but within its mission to "to organize the world's information and make it universally accessible and useful" ie. to know everything about everything, which I'm sure tracking plays a role in.