First off, this is all my opinion, not absolute truth.
Second, sure Amazon does ads on the side, but the majority of their money is made by selling their own products. Occam's Razor suggests that they simply want to sell you stuff using one more way. Notice that the Echo didn't do almost anything when it was initially released, except allowing you to buy stuff. That was the part that they worked out before launching it.
Also, don't forget that Amazon also has a number of other devices that are very similar: the Dash button and Amazon Fresh come to mind. The Echo fits nicely in line with it.
I am not saying they couldn't use it for something nefarious: they could definitely abuse it. I just think that they have less incentive to do so than Google.
Second, sure Amazon does ads on the side, but the majority of their money is made by selling their own products. Occam's Razor suggests that they simply want to sell you stuff using one more way. Notice that the Echo didn't do almost anything when it was initially released, except allowing you to buy stuff. That was the part that they worked out before launching it.
Also, don't forget that Amazon also has a number of other devices that are very similar: the Dash button and Amazon Fresh come to mind. The Echo fits nicely in line with it.
I am not saying they couldn't use it for something nefarious: they could definitely abuse it. I just think that they have less incentive to do so than Google.