They do, and Google for instance has a huge number of servers supporting YouTube, but in this area AWS delivers cheaper and better than its competitors.
Google has 7 US data centers. AWS has 27. That means your video is closer to the consumer and can be delivered faster and cheaper. Everyone goes to AWS, letting them build even more data centers.
Never had any delays streaming videos from YouTube. All this talk of “streaming faster” and what not...does anyone even notice the difference?
Not to ment6n Google and Microsoft are richer than Amazon is, with much more profits. And Microsoft has been closing in on Amazon in cloud market share over the past 10 years.