To be honest, your question is set up in a dualistic fashion. Like, there is only the Bible's take and the "Devil worshipper's" take, which is in itself very narrow and ignorant of all the various other takes out there. If you want to know why people would want to communicate with "demons," you should ask why anyone would want to speak with an angel, deity, spirit, ancestors, elementals, entities, etc. Christianity didn't invent the term demon; they just rebranded it, like they've done everything else that didn't fit their own cult's narrative.