Each would need to keep track of the subscriptions, meaning more resources that would mean higher cost.

They need to do it with unicast, which necessarily takes more resources to do. Think of it, 500 unicast stream or a single multicast stream, it's not even close how much less computing power multicast takes.

Make no mistake, multicast is broken by choice. Working multicast is "contempt of business model", it would cannibalize CDN profits to become as free as unicast.

the same systems to produce effectively the same improvements.

One crucial distinction is that you as an individual, will Zuck's permission to use their system, in their way, in their rules.

And of course by "Zuck" I mean, "the cloud" aka "someone else's computer", which was not needed if multicast did just work, another enforced cloud dependency

1/16 of all IPv4 addresses were reserved for PUBLIC USE but they remain firmly in the grasp of private hands, private hand that want you to pay the toll and obey their masters

well just ask how the ip6 upgrade is going.

My GPON FIBER ISP said "we'll probably never implement IPv6", even though every single piece of equipment on their network supports it, even their horrible rebadged Huwawei routers

It won't work and it will keep not working until we make them.