Buy a loudspeaker; get a free mainframe

Amazon is no stranger to bundling their products.
It's a way to get you into their ecosystem, or partner with third parties they like.
Usually these discounts are OK, and can be filed under "well, I was going to buy these products anyway, might as well get the deal."
In this case, though, Amazon is providing a substantial discount when buying the Echo Tap and Fire HD 8. Individually, these products cost $129.99 and $89.99, respectively. Amazon is currently selling them both for $129.99.