Your views on how religions were "designed" seems flawed. You're making it sound as if concepts were added or modified just like that, when in reality, a spiritual belief mutates as people's beliefs change (for whatever reason eg. it could be a priest telling them or a vision someone has through use of psychoactive substances) similar to how science iterates. For people who believe, their spiritual experiences are as real as gravity, as much science as an article in Nature.
You can see this mutation I speak of if you've ever been part of a newly-made religious group. Similarly, it can also be easily visualized if you're part of any subculture as it evolves.
> why would anyone choose to believe in a negative afterlife as opposed to none at all
I'd like to point out belief is not a "choice". You don't choose to believe in an afterlife, for example, you either believe in it or you don't. You can, obviously, modify your beliefs in many ways, but ultimately, it's not as simple as a choice.
Well, some beliefs are choices. "I will choose to believe you." seems like a sentence that can actually be true.
I'm not sure that with enough practice, one wouldn't be able to simply choose to believe whatever they wished to believe. To be able to believe, if they so chose, that the moon is truly, and not metaphorically, made of cheese.
I am fairly confidant than one can create emotions within oneself, which are simultaneously both sincere, yet also not the ones that they would have felt by default, had they not chosen them.
I don't see why the same would not be the case for beliefs as well.
That is not to say that most beliefs people have are by choice, only that some beliefs are, and probably any could be.
> why would anyone choose to believe in a negative afterlife as opposed to none at all
I'd like to point out belief is not a "choice". You don't choose to believe in an afterlife, for example, you either believe in it or you don't. You can, obviously, modify your beliefs in many ways, but ultimately, it's not as simple as a choice.