How might one sway the evil to change their ways? Perhaps by promising a holy man's paradise if they were to? Heaven, in its base form, acts as a bargaining tool used to encourage good behavior. And yet, one might wonder, do satanists1 want to go to hell? By the logic of worshiping a deity, would one not logically want to go to the domain of the deity? Then, compound this with the concept that one should follow the deity that they most align with, and the swaying power of heaven is all but gone. Heaven is wasted on those who need not be swayed.
Heaven is for the holy, only. Holy is a term that is inherently subjective. What does one deem morally right? Is one man's holiness another man's sinful folly? In at least one example per person, the answer is yes. So heaven is for the holy, but each man has a personal holiness that he adheres to (not to say, of course, that these concepts of holiness cannot be shared, for that is the basis of organized religion, an establishment of morals and seeking to spread them), ergo each man has a heaven that he seeks (excluding atheists and agnostics, who have no defined heaven, or none at all). A concept of heaven only applies to those who believe in it, and by way of believing in it, they are bound to try to achieve it (whether or not they do, no one can say, but let's assume they do reach it), so by that reasoning, heaven is only achievable to those who will already achieve it. What then is the purpose? None, heaven is wasted on these believers. Heaven is wasted on the holy.
1. I'm aware the term "satanist" can be extremely broad term, but I was using it in the very most basic form, which would be someone who takes Satan of some form as their deity. Apologies to atheistic satanists and those that might be offended by the far-reaching nature of my description.