In most supernatural horror movies, especially religious ones, the characters will fight evil spirits and entities, the Devil being one of the most popular ones. However, what confuses me is when he does soul deals, birthing the antichrist(s), possessions, terrorizing, etc. Why would the Devil interact with just normal people who, especially to him, are random nobodies? Maybe if it was a low demon doing it, that is understandable, but why would the big bad waste his time, when he could do bigger and more powerful people?
Someone who is already powerful or important either made a deal with the devil to get there or doesn’t need to make a deal with the devil any more.
There’s also the trope that the rich and powerful are already corrupted and their souls belong to the devil without any action needed by the devil.
On the other hand, the downtrodden humble person who has led a mostly good life and never been corrupted is a person the devil might take interest in to try to take a soul that is destined for heaven.
From a storytelling perspective, if the target of the devil wins and we are sympathetic to them, they should be a low character, everyday person who manages to succeed. That is the basis for comedy: the low brought high. If the devil wins then the victim should be powerful and successful. That is the basis for tragedy: the high brought low. Those two concepts are over 2,000 years old and go back at least as far as Aristotle’s Poetics (a treatise on how to write good dramas). So the out-of-universe answer is that it’s good storytelling.
For horror, it’s more horrific if most people can put themselves in the victim’s place. If horror movies only happened to rich and powerful people, we wouldn’t be horrified, we’d be more likely to think they deserve it and it would never happen to us. For us to feel real horror, we have to see ourselves in the place of the victims.
Why would the Devil interact with just normal people who, especially to him, are random nobodies?
But what do you consider a special person to the Devil? It doesn't need money or power, the key resource it looks for are souls.
If a person has already sinned a lot, it's not of a big interest to the Devil, because it already owns this soul. Thus an average person, whose fate yet to be decided is worth more effort, either to convince this person to sin more / sell the soul or challenge his/her existence and make it unbearable to the point where this person commits suicide or gives up his soul to the Devil.
When a character interacts with random people and does random things, it builds the character.
A couple of scenes that come to my mind is:
- In the movie No Country for Old Man the assassin drives his car across a bridge and he randomly shoots a bird.
- In the TV show Fargo the mob hitman convinces a teenager to urinate into the motel manager's car fuel tank AND this hitman calls the manager telling her someone is pissing into her car.
Both characters do random things that are irrelevant to the main plots but they help build their characters, being playful, ill-intended, intelligent, etc.
The theological answer is there is no one beneath Satan's notice just as God sees every sparrow fall. Moreover, Satan is not limited by mortal constraints -- if Santa Claus can visit millions of homes and spend time in each one in a single night, we are forced to conclude that Santa (and Satan) can bilocate like crazy.