We don't know why Lucifer rebelled. We're not even sure if he was really an Angel at this point (Biblical Lucifer was the mortal human king of Babylon), though it is strongly implied that he was.
There is a body of pop culture that associates Lucifer with the Firebringer/Lightbringer archetype as exemplified by the Titan Prometheus, a character who elevates mankind by teaching them the forbidden knowledge of the gods, thus earning the enmity of the gods and an undeserved punishment. Perhaps his original attempt to create demons was purely altuistic, an attempt to free humanity from the cycle of life and death, that went horribly wrong.
We also don't know if God with a capital G actually exists. Angels do not imply a God. All we know is that there are gods, lower case plural. Most likely the big throne goes to the head of whichever Pantheon is on top at the moment.
That would give us either YHWH, Allah, Jesus, Brahma, or Buddha, with the Yellow Emperor having only a distant shot at the position.
YHWH is an asshole who betrayed his wife and cast her aside like so much garbage because he was jealous of the worship that she was getting.
Allah betrayed his entire Pantheon and stole YHWH's shtick.
Brahma is also sort of a jerk sometimes, but he isn't as egotistical as the former two.
Jesus, Guatama Buddha, and the Yellow Emperor was interesting case because they were all mortals who became gods because they were so incredibly awesome.
JC was a devout YHWHist who may or may not apreciate being elevitated to divine status.
Buddha didn't really care about wordly things and spent most of his efforts transcending existance by purging himself of all desire. He's also an aescetic who gave up his throne to seek enlightenment, so it is unlikely that he'd seek the throne of Heaven.
Now, the Yellow Emperor is more than a little baddass, being the first Emperor of China. But it's unlikely that he sits on the throne of Heaven simply due to the fact that he'd play a much more active role in things if he did.
All current information suggests that the Throne of Heaven is currently vacant, with the four politically powerful Angels using "God" in the same manner that The Party of 1984 used Big Brother, a fiction that justifies their power.
Either that or the current holder of the big title is a paranoid recluse, which certainly wouldn't be a good thing, either.
There is actually no evidence that human souls naturally go to Heaven or Hell, and the Reapers appear to be a neutral third party who aren't above taking gods. Most likely, there is a separate land of the dead and everyone in Hell either damned themselves by making a deal of some sort (some more innocuous than others) or were damned by others practicing dark magics.
