They don't seem to be p2p either, they have some server. Maybe it's stolen infra.
Unless there's some kind option where youtube or twitch signs a contract with select creators and then hands them huge sums of cash upfront for the costs of future content production, or to license the creator's existing content to distribute via youtube/twitch then the cost of getting that content is still just as free for youtube/twitch as it is for the pirate streamers that upload bluray rips.
Ad revenue is money gained from advertisers at the expense of viewers, it's entirely separate from the cost of the content being viewed.
b) you find the hosting where you can just pay for bandwidth
c) the bandwidth is actually cheap, until you hit petabytes of traffic or dozens gb/s of BW
d) you don't scale for millions, you scale for hundreds, maybe thousands
EDIT:
e) most users of such sites aren't demanding for quality nor service, therefore you can compress a lot more and if you overloaded they would come to other sites (which could be operated by the same people just serving from the other place)
Actually, the opposite is true.
If you live a country where piracy is persecuted and these services aren't available and you want to watch Silo, you don't have a choice — you have to pay for Apple TV. If you want to watch Stranger Things, you have to pay for Netflix.
But if those services are available to you, then you would have those shows on any of dozens of pirate services, and you can switch between them anytime. At which point they actually start to compete on other qualities, like streaming.
In fact, many of them have much better quality, at least in the areas where their audience lives.
It's not 'opposite', it's some people care but most are don't. You can cater for those who care, but that means costs in services and people, or you can ignore all that noise and print money from Regular Joe, who bought 15-in-1 DVD mere a decade ago.
Bandwidth might be cheaper in absolute terms, but you're not paying less per user than if you scaled higher. How do you go from there to "the business model is to not scale up"
Except you need more money thrown in the hardware to be able to utilize that bandwidth. It doesn't scale linearly. At some point it's easier to setup another node to handle another 10Gbit and while you now pay double the node cost , now you can actually scale horizontally, because it's easier to serve the same content to different people from many nodes than from one big fat one.
Also, you need clients who would watch your content and would give you ad views and hence money. If you pay $1000/m more for another 10Gbit for each node in the first place then it's another $1000/node you need to get each month.
Remember, this is not enterprise customers, with $/user costs, this is profiteering from a highly fluctuating and risky market of solving the service problem... without paying the IP holders anything. Though that's a B2B service problem too, but it wouldn't be solved till corporations' greed would exist.
