Because the requirements are different. Royalty inhabit places designed to last thousands of years (castles), and they are known to be dreadful to live in. Stone walkways and stairs wear and become uneven, shifting foundations create little gaps for drafts to flow in, modern conveniences are difficult to install, if possible at all.

It is better for living humans to inhabit spaces that can be replaced and updated over time. The dead need things to stay essentially the same, and they don’t wear down the areas they reside in.