There are certain protections that apply to libraries as public institutions. I wouldn't expect any of the others to be private. The rationale for why the postal "metadata" is not private is simple: no one can reasonably expect anything they write on the outside of an envelope and then drop in a box for potentially dozens of people to handle to be private. That same reasoning can be applied to phone numbers, text messages, e-mail addresses, and URL's. If I'm disclosing to Google what URL's I'm visiting by typing them into Chrome, I can't complain if the government can access them too.

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.