This is D&D. Pretty much anywhere else you die, you go to one of the outer planes, which are, pointedly, not in the control of any particular deity. You have the option of going to a deity's realm, but if you're LG, you still go to Mount Celestia, even if you were an LG character who refused to worship deities or an LG character in a world where all the gods were dead and mortals were living in their abandoned metallic husks, or an LG character where the only god in your world is a massive sucking evil at the center of the world.
The FR pantheon, by being a subset of that cosmology, made an explicit choice to not allow that. They decided, no, if you're an LG character who refuses to worship deities (such as an honorable dragonborn who thinks that worshiping gods is for chumps and slaves), you get a rotten afterlife.
FR could get away with that if the only afterlives that existed were the domains of the FR deities, but that is not the case in FR.