Just to clarify, I’m not advocating for hedonism. 
I’m just saying that it would seem like a somewhat logical choice if there is no heaven, hell, purgatory, rebirth or any other kind of afterlife to just “make the most” of the current short life. I believe/accept rebirth, so have no interest in hedonism.
But for those that do conclusively believe there is no afterlife of any kind (putting aside the endless debates about self, no-self, soul, no-soul), why not just pursue happiness all the time, whatever that may be for the person believing this. If they are right, there will be no repercussions.