Sab,
Yes, you're right - you would think that superior intelligent creations would do something purposeful with their life - unlike humans who come under the ransom sacrifice, the fallen angels do not - they know they have a death sentence hanging over them and there is nothing they can do about it.
When you're created perfect and sin wilfully, there is no place to go but down.
Some fallen angels delight in terrifying people because they can do so and they have plenty of free time since they no longer carry out their original assignments.
Consider the info at this link: http://www.nightwatchmanchronicles.com/INT/DianaPossession.htm
The bible makes it clear that Satan is good at deception. Those that believe in him, especially the demons, fear him. Others that don’t believe, he either makes believers out of them, by having his demons have some fun at scaring them. That’s how the demons view it. They do things and then watch for response. If your hair goes up on the back of your neck and your pulse is racing, they get a good laugh out of terrorizing you. If you could see them do it you would be angry at how funny they think it is to screw with you.