Why do demons do what they do?

[Deaxsa]

Fair enough, though a lot of them are highly intelligent. I guess what I meant is, why go for temporary destruction when they can do something more permanent? Succubi got that down, for example.

Because the concept is alien to them. They could not plan world domination any more than all the cockroaches of the world could. You must remember where the demon comes from: basically the embodiment a concept (luck demon, lust demon, starvation demon, etc). These are living, breathing qualities, not people. Now specific systems will probably try to make them fit in one way or another, but then you must look to the system for their reason.