Because it's fake. Look at the images. There's a LED above the volume down key, F keys (F1, F2, F3...) have blue text and the bottom is made of plastic instead of metal. Look where you insert the battery.
It certainly looks like the real thing at first glance, but I wouldn't be surprised if it doesn't feel right or breaks so soon you have to replace it and don't even actually save money.
I'm personally using a wired Apple keyboard with numpad from 2008 and it still feels brand new. All keys still feel perfect, no sign of wear and it's still being sold right now. The $49 investment was definitely worth it, and I can't say that about all the peripherals I've bought.
It's a great alternative to the $69 wireless keyboard if wireless is not a necessity (and it rarely really is).