You don't need a warrant to get data from a third party. The government just asks and if the they enjoy receiving special treatment and other favors in the future they comply. That's why the USG likes to have this collection devolved to private entities.

> You don't need a warrant to get data from a third party.

https://policies.google.com/terms/information-requests

"In all cases: Issue a subpoena to compel disclosure of basic subscriber registration information and certain IP addresses

In criminal cases:

Get a court order to compel disclosure of non-content records, such as the To, From, CC, BCC, and Timestamp fields in emails

Get a search warrant to compel disclosure of the content of communications, such as email messages, documents, and photos"

Some 3rd parties require warrants. I tend to think that this is the rule rather than the exception.

Google isn't the one holding the keys to the castle. Data brokers predate them by decades. The primary reason why the US has weak data protection laws is because the government doesn't want their activities to be encumbered.

Your assessment is only correct if the warrants are not obtainable at will.

Edward Snowden and the FISA court say hello.

If you don't know about it, they don't need a warrant.

Says NSA.