Why don't our emails show you what we're selling?

dave thought this was worth mentioning said

Every day we send out a Meh email that highlights the day’s deal. Or does it? It steadfastly refuses to reveal the actual thing we’re selling.

What’s your theory for why we do that? How would you explain it to a friend who asked you? (Feel free to tell us if you love that we do that or hate that we do that, but I’m more interested in your thoughts about why we do it.)