It’s like saying everyone has heard of atheism, so why isn’t everyone an atheist, or everyone has heard of a type 3 civilisation, so why aren’t we one yet? These things are a combination of letting go of old beliefs (which some people refuse to do, so generations literally have to die before things change), technological progress and changes in existing power structures and incentives for those in power who the new system would displace, who are going to fight to keep their power despite what is best for humanity overall (if they even have the perception to see that).