Why can't we bury the coffin after death?

People in most places still have to be buried after death, and only a few places have the custom of hanging burial. Why do some places bury their ancestors on high mountains and cliffs? Some people think: "High mountains and dangerous land can prevent people and wild animals from intruding, and can let ancestors rest and sleep forever." Some people think that "the cliff tomb is ventilated, sunny and dry, which can be beneficial to the long-term protection of coffins, corpses and martyrs." "Our ancestors were buried on the cliff and looked at us like stars and the moon, and future generations will prosper." "It is the attachment and belief of the deceased to be surrounded by mountains and waters." "The higher you are buried, the closer you are to heaven, and the faster you will ascend to heaven." These ideas can be found in some ancient books.