I suspect from the tone of the email that the manager may have already tried that route and gotten pushback. It feels very much like a manager who is tired of the excuses and trying to be as unequivocal as possible so as to be 100% clear.
And that's assuming we even have an accurate statement, which is a big assumption. Aside from the missing context, we frankly don't know that any of this text was written by the manager.