There aren't many barriers to entry in this field though. It's not a situation like a utility/ISP where you can only feasibly have one last-mile connection due to permits or limited radio spectrum. It's not even something like a nuclear reactor which costs $10B and a decade before you can flip the switch.

I'm not saying I could build a streaming site in my closet this weekend, but it's not impossible for competitors to enter the space (or existing competitors to grow in the space) so long as Google/YT doesn't too anything too anti-competitive.