This is more akin to a safety deposit box. The bank doesn't necessarily know what's in there. It's not the same as compelling testimony from a housekeeper.

Sure, Facebook/Google have more access than a bank has to the safety deposit box, but the likelihood that anyone at Google or Facebook has actual knowledge of the information the government is looking for is slim to none.

Maybe a better analogy would be a warehouse. Just because things are stored in the warehouse, and employees have access, doesn't mean that the employees have rifled through them.