It was because there were already people in a tomb possessing up that role.
So Xia Feng could enter it easily by reaching out for a connection to his own inheritance. As A Reincarnation Emperor, Xia Feng was simply bound to get that power which belongs only to him. It wasn't like no one could wield a rule, however.
Xia Feng could be called an origin of that power, but he would surely need to work a little if someone had reached out for that power before him.
Just like everyone could recite an unknown paragraphs to reincarnate, only Xia Feng could perform the best reincarnation that had given him an unique body without any impurities of a bloodline - he was like a true god.
No one had the same bloodline like Xia Feng, even his daughter.