I don’t think it has to do with not paying rent or anything like that. Mitzrim and in our days Chinese and Russian commies keep their leaders awashed in chemicals for the show – and I heard those are not smiling. Of course, it may be these mummies are not smiling because they know they are destined for gehenom or because they look at the current rulers of their countries and lament their inability to rule the country with a really strong hand.
Presumably, the skeletons you encountered are beinonies, so it proves that Hashem has chesed to an average person aharei hamitah. Good to know.
In truth, you cannot say “always smiling” because you didn’t see all of them – and all the time. So, your question will be re-asked during tehias hamesim.