My paraphrased interpretation of the email is that he's not going to send out books to people who don't want them, or won't review them in a timely manner. I understand that "timely manner" may be subject to debate, but ultimately the publisher is sending out ARCs for review as a means of advertisement and publicity to hopefully generate sales on the initial run of hardcover copies where they actually have a measure of profitability.

That said, I don't see any specific reason for the limitation to three titles per month: to me, that smacks of laziness in being unwilling to handle the abilities of individual reviewers to read and produce a review (in the aforementioned timely manner ).