The simplest explanation, by far, would be a deistic view of some sort or another from which questions of the meaning of life cycles immediately emerge.

A belief in natural emergence relies not only on endless untestable hypotheses, but even still results in the exact same sort of frustrating unanswerables. For instance if one believes that the initial matter, which would culminate in the Big Bang, whisked into existence through a quantum fluctuation, then it immediately leads to the question of what created this void, rich in quantum interactions, or the nature of quantum interactions themselves? And for that there's not even a hypothesis, untestable or not.

Maybe there will be one day, but also maybe not. To me the simplest answer is to simply acknowledge of our own inability to offer any compelling answer to this question. That's not to say an acceptance of such inability, but assuming the nature of a destination (one way or the other), in a journey we've yet to even scratch the surface of, seems neither simple nor wise.

The scenario of a created universe doesn't itself give you any kind of reincarnation or afterlife. It's added complication, especially since every aspect of it is apparently hidden from us in elaborate ways.

I mean we are on HackerNews, site filled mostly with rational, down to earth people. But there are billions people that believe in, for example, saints that can intervene in the earthly affairs. They also believe in multiple stories about miracles involving that saints after their death. I don't, but your razor doesn't work when one believes there is evidence to the contray. In fact, despite our bubble, way, way more people worldwide are religious than atheists.

(and by the way, you only picked two out of many questions to answer)

That seems to imply those billions of people religious are not rational, down to earth.

Theism in itself is a simpler explanation for existence than atheism, and yet many rational people are atheists. Is it because they weighted all the possibilities or because they discarded the option a priori?

We are all way less rational than we would like to believe.

I would argue that theism is not just a simpler explanation but a more naive one.

We could also explain computers as magic and it would be simpler than explaining it with electricity and math.

No religions are based in any observable facts* and thus being naive explanations, indistinguishable from magic.

* More like they are based on deprecated observable facts, at first the sun and nature, later man and it's dramas. Now we now the sun is just a big ball of gas and man is just a big brained mammal.

That being said religion is just one area of many and you could be very rational in lots of them but be religious for whatever reason.