You get more of the behaviors you encourage and less of the ones you discourage. The US legal system strongly discourages retaining email, since it rarely works

You get more of the behaviors you encourage and less of the ones you discourage. The US legal system strongly discourages retaining email, since it rarely works in favor of the entity making the retention decision. And there is no particular reason to keep emails that old, so naturally companies want to get rid of them.