Here's the situation: you get a hireling. They e-mail you stuff. It's all lovely.
Then you get busy. You have work, papers, exams, school, a social life, get the flu, whatever. You don't quit playing the game. You don't come here and start a rage thread. You don't quit paying your monthly subscription. You just get busy. Several days pass and you didn't log into the game - and now you've lost all those mats.
So you have to think about logging in every single day just to read 4 or 5 e-mails from 3 toons? It's isn't unbearable, of course, but it can be an inconvenience and it does make the game a bit less fun and a bit more like ... work.
But wait! Isn't this capable of abuse? Abuse! Abuse! Abuse!
Is it? Really? I'm paying for the game, right? I get exactly the same amount of materials of I take the time to log in every day versus Zeni sending letting the e-mails stack for, say, a week? Then if I don't log in within a week, then they start dropping off.
C'mon, Zeni, have pity on us are busy. Let us stack a few e-mails, at least.
Valar Morghulis.
Someday I'm going to put a sword through your eye and out the back of your skull. Arya Stark
You're going to die tomorrow, Lord Bolton. Sleep well. Sansa Stark
If you are neutral in situations of injustice, you have chosen the side of the oppressor. Desmond Tutu