Internet2 was suppose to wholesale replace what we have now with IPv6 until they realized people and businesses were not going to shell out the collective trillions to pay for it. Remember back in the 00s they kept saying IPv4 addresses were running out so everyone got creative with private network space and told them to fuck off.
https://en.wikipedia.org/wiki/Private_network
Fun fact, Internet2 was supposed to set up with ID and licensing per user so 1) no anonymous usage and 2) mark of the beast shit to cut you off the second you said kike in public.
(((ietf))) loves to shit on NAT but the internet literally IS NAT. It requires NAT to be "internet", the word givs it away "internet, noun, network of networks" not "one global network where your identity is your MAC address and your IP has your MAC address embedded."