Here's a semi-official response about the annual reports from the data team, a.k.a. "the stats helper monkeys":
We wanted to make absolutely sure that the blogs that received these recap emails had the right mix of activity to make it likely their authors actually wanted them.
Knowing how offensive it can be to receive an unwanted email, we only picked a few blogs to get the email, blogs we were sure would most definitely be thrilled with the annual recap email. The bottom-line is, our helper monkeys were afraid to email blogs unless they had a mixture of many different activities.
Clearly we made some mistakes, and we’ll fix them next year.