The whole laymans interpretation of Ancient god kings even were is sort of off, right? Like, ok, first you mostly get it from polytheistic cultures. If one had power over somthing, it was a niche. You don't make offerings to the goddess of the hearth for a bit more rain. You have you pantheon which people focus on what benefits them most. If you're sufficently rich, you have your shelf representing all of them.
The king - or whatever the local term is - wants to be represented on that shelf. There are things the king wants to be acknowledgment as the authority on - not everything, but some of it. How much acknowledgment is based on competition - not with the gods, but with other kings. If the pharaoh or emperor is to be worshiped, it's because all local human opposition has been dealt with. It's because there is nobody more powerful to compare to.
Monotheists don't have that same feature in their rulers. There is no shelf of peers to add them to - so either you have a conflict because there is no shelf, or you have the mandate of The god. The king