If you will permit my interjection, it seems to me that there is a fourth reason. The nature of gods being what it is, all parts of the dwarven character will find their mirrors in the gods. Dram's "drunken, violent, disruptive, argumentative and stubborn" character are, though distasteful, undeniable aspects of drarven character. By embodying these aspects, Dram takes that burden off of the other gods.
"By being the worst of us, he allows us to be our best."