Because those are the underlying services that the above software is built on. And they allow the system to handle both very few to many many requests/sec for basically $0. That's the point of the article.
To say, "I can run a server that can handle a bunch of requests for free" doesn't mean much. Of course you can do that. But can you replicate the aforementioned system for free? Probably not.
To say, "I can run a server that can handle a bunch of requests for free" doesn't mean much. Of course you can do that. But can you replicate the aforementioned system for free? Probably not.