I don't recall Google ever promising to be a "pure" web search engine, just indexing all the pages.
Quite the opposite, they said the goal was to organize and present information. The goal has always been the most relevant information given the query. Early on, that pretty much always meant a web page. More and more, they already know the answer and can present it with a better UX for the user.
Why should they be required to be a "pure" index of web pages?
I'm not sure it's really the same. Someone asks Google "how far is it from Portland to Austin", and before they got 10 blue links, and now they get a number. That's not the same as "amazon, send me some Coke" and them sending Amazon brand cola drink.
Quite the opposite, they said the goal was to organize and present information. The goal has always been the most relevant information given the query. Early on, that pretty much always meant a web page. More and more, they already know the answer and can present it with a better UX for the user.
Why should they be required to be a "pure" index of web pages?