So, get this.

Sun always had his kingdom with over 40,000 different monkeys and apes to look after. They were his most loyal and loving subjects and did exactly as asked all the time, they were pretty much his life, though he'd leave often in search for ways to become immortal, which results in being gone up to 20 fuckin years or more.

But every time he came back they'd be so happy to see him and they'd celebrate his return with a feast. So it was always a huge party. And at one time, Sun sobbed cause he feared for their deaths and shit, and at some point, he erased his and their names from the Register of Life and Death, basically they're unable to die. So...

after 500 years under the mountain, he probably tried going back at some point only to not find any of them there. So...... idk, I always think Sun believes the world's against him and his fam always backed him up. They called themselves the Sun Family so...
Damn.