Why Fiends rarely enter the prime material plane overtly:

[Monty Tomasi]

There could be billions of Prime worlds that have been invaded by fiends and reduced to ashes. But does anyone really care?

Sure the Celestials probably have a list of all the worlds that have been lost to fiendish machinations, however it'd be pretty depressing reading and the Celestials are unlikely to publish the list any time soon (especially if they keep needing to revise it).

 

[Nightfall]

/me pulls out Rappan Athuk...

Yeah well that was just Orcus' idea of a joke I think.

 

[Ambrus]

Honestly why should fiends ever bother? Corrupt mortals keep dying on the prime all the time and so they constantly pop up in the abyss as petitioners. Fiends are already knee deep in dead mortals; they don't need anymore really. Fiends could come to the material plane more often but the mortal races seem to be doing a fine job of starting wars, fighting each other, doing evil and growing corrupt all on their own; is it really worth the effort to go there and kill them yourself? Why dive into the water if the fish are already jumping into your boat?

Hell, with all those mortal wizards and priests constantly summoning fiends it's hard enough to keep out of the mortal plane!

 

[lukelightning]

I take a page out of the Warhammer universe and say that fiends are unstable and can't stay on this plane for any length of time without special binding magics, magic circles, etc. to help them stay manifest.

 

[prosfilaes]

I know this is a simple question with a complex answer, but what's so pressing on the Lower Planes that they'd want to stick around there for? Isn't one fortress made out of skulls and mortared together with the congealed bodily fluids of the damned pretty much like another?

Isn't one European castle just the same as another? Why did Germany and France keep attacking each other, instead of going for Asia or Africa?