What product are you referring to? I'm in this industry and based on my experience their video encoding+storage+streaming offerings are actually higher priced than their competitors. The reason their services are popular is the integration with the rest of AWS (which is true for most of their offerings).
The only cheap thing that Amazon offers is fast shipping for low-cost products, e.g. buying a $3 cable and getting it shipped for free the next day (assuming you have Prime). But for anything above $50-$100, Amazon is almost always the more expensive option.
https://slate.com/technology/2013/10/amazon-book-how-jeff-be...
The whole point of predatory pricing is that you jack the price up if you don't currently face any competition and use the threat of plunging prices to scare off competitors, so of course they're going to be more expensive by default.
Take the encoding example above, you might pay a competitive price for the compute time required to encode, but you'll be paying some of the highest bandwidth fees in the industry if you were to stream out your encoded video to multiple viewers.
Where electronics are concerned, for years I would go to Best Buy to look at merchandise first-hand, then go home and buy it from Amazon, because Amazon was almost always significantly cheaper (especially before they started collecting sales tax).
Now it's the opposite.
I use Amazon to find products, read reviews, etc., and then I go to Best Buy's website to order it. It's almost always the same price or lower at Best Buy, and since I happen to have a Best Buy store only five minutes from my house, I can order it and pick it up in under an hour.