I disagree with you, but from the perspective that my email contains the history of every transaction I have ever made, all of the newsletters I sign up to, and, for another 3 days, ~50% of my conversations, since I do a good chunk of my communicating over gChat.

Consumer preferences change over time, so google is far more interested in the thing I bought yesterday than the thing I bought 4 months ago, so being able to read my emails is still a current interest of theirs.