Why is so much of IPv4 allocated to multicast when it cannot be used by the public at large ?

I found the multicast registery here.

https://www.iana.org/assignments/multicast-addresses/multicast-addresses.xhtml

I already knew that addresses between 224.0.0.1 and 239.255.255.255 are reserved by multicast.

Obviously multicast could be immensely useful if used by the general public, it would obsolete much of facebook, youtube, nearly all CDNs (content delivery networks), would kill cloudflare and company's business model and just re-arrange the internet with far reaching social implication.

So, why hasn't all these multicast addresses been converted in usable private IPv4 unicast address space ?