the Devil can't do anything without our consent and that is why they're obliged to tell us

The reason the worshippers of Evil keep on telling us the truth, through the entertainment industry, is usually explained in two ways, where one does not exlude the other

Some say that the Devil can't do anything without our consent and that is why they're obliged to tell us, like a warning, so if we still don't do anything about it, it is actually,
our fault: our choice

Some others, say that they have to let us know what they're doing, so that the karmic consequences do not come back to them.
In the occult, this is called the "revelation of the method".