>>5000730
I also thought it had something to do with royal inbreeding or intermarrage since it became prevalent for higher nobilities to "preserve their heritage". There were methods on arranged marriages to keep political alliances among elites which was seen as union of lines rather than a contract of individuals at the time. And enforced others that 'this must be so' onto how an english dialect is spoken. Mind you, I'm not being brash but there's plenty of evidence from oil paintings of old that'll explain more than a thousand words.