There is this idea among hackers that you should be able to trust Google, etc, to keep information private from the government. But that's not what privacy means in the context of the 4th amendment.
The 4th amendment starts with: "The right of the people to be secure in their persons, houses, papers, and effects..."
It's clearly referring to things that are truly private: things you keep in your house or on your person, not things you voluntarily share with potentially hundreds of people at AT&T, Google, Apple, Akamai, etc.
How many people realize they're (with the default configuration) disclosing to Google what they type into the address bar?
By your rationale, there is no warrant necessary to search the secured offices of a corporation that employs an outside cleaning staff.
Do you think it's appropriate to evaluate the meaning of "privacy" through what a 200-year-old document says? Or do you think we might need to take the Internet into account too? Does privacy have anything to do with what laws say?