Earlier IP migrations were done when the internet was run by universities and government bodies who felt the need to migrate to a newer standard because there w

Earlier IP migrations were done when the internet was run by universities and government bodies who felt the need to migrate to a newer standard because there was a newer standard. IPv6 took longer because the internet is now run by companies that need to see a return on investment, and as long as IPv4 was working fine for their customers, didn't see a benefit to it. It's why IPv6 adoption only started taking off when the answer to "Our projected customer growth this year is 200,000, can we have 200,000 more IPv4 addresses please?" became "No".