I have no idea. My knowledge of ancient Chinese historical practices comes mostly from learning various old texts and their background. My example "the King of Liang" comes from having read a text in which Mencius speaks to a certain 梁惠王 about benevolent rule.
I tried finding sources. I got one that says just King Hui of Wei was just called King Hui of Liang posthumously, though the only source I found that said Wei was also called Liang is Wikipedia.
It's pretty fascinating how Imperial China, despite leapfrogging past feudalism in a dynasty, still placed such emphasis on familial ties. I mean certainly the family is the basic unit of society and all, but if the government was already based on meritocracy (in theory), why should there be an emperor still? Would not such a figure be constrained by his own blood ties at the expense at his capacity to govern on behalf of the state? Your idea is cool and reminds me of the Roman practice of adopting imperial heirs.
To be concise, the government became meritocratic, though of course not totally meritocratic to be honest, as a tool of the Emperors. Initially, before the civil service exams became prominent, most officials came from the nobility. That was why the bureaucracy was more often dependent on the rulers than the other way around. You might ask why the Confucians followed the rule of a monarch in place because of blood ties, but that idea is an old one regarded as legitimate for a long time.
Also, regarding the idea of heirs outside of the imperial family, I can think of only one example of an adopted son succeeding his father to become a ruler, but this was only for a short-lived, small, northern dynasty.