It's basically just them deciding to use aws as a service provider rather than buying and maintaining their own servers or using another cloud provider (eg. Google, Azure). Whichever the case, stronger infrastructure for the consumer (assuming it is stronger, likely this comes in the form of a discount on compute units in exchange for their large volume of business). Stronger infrastructure means availability for higher res (bitrate and/or resolution), scalability (less down time, dropped frame etc). Overall it's less likely they will pass the savings down to the consumer than they would accept the discount on services compared to other options.

Tldr blah blah blah