The thing is, a great number of pantheons are more caught up in their own intra-pantheon wrangling and battle. They have their own “good” gods and “evil” gods. And the games they play with each other consume most of their time an energy.
You don’t see much intER pantheon fighting as it can be very destabilizing. Rules of the game are typically mutually agreed upon within a pantheon, going outside the pantheon, all bets are off. It can be deadly, it can be dangerous, it’s unknown. Too much of risk, usually, unless you are certain you can capture more worshipers.
And in fact, that’s what most intER pantheon rivalry is. It’s fought between worshipers on the ground, i.e. by proxy, rather than directly. It’s a cold war between the pantheons.
We demons are, by and large, outside any of the pantheons (yes, there are some definite exceptions). But as a rule, the Demon Princes try very hard to keep demons from screwing with any gods or their factions. We want to remain a neutral force of Evil. If that makes any sense.
We often provide a place of refuge for those fleeing the games of the gods. There are definitely some demons who are “fallen avatars’ of various gods.
There are some refugees of these battle who hole up in the Abyss, because it’s generally not worth the effort of their enemies to pursue them there.