I assert that this is the result of religious conditioning, even among people who have rejected religion.
I don't think so, I think the pre-disposition to search for purpose and meaning is natural to all humans. It is probably also a source of many scientific discoveries, to look for inherent order in the universe in order to get a glimpse of the overall scheme of things has probably been a great striving force for many scientists. Then what form that search takes may depend on various things, including religious conditioning, but religion itself was probably created
because of that need (not the other way around). It might be tempting to think that religion was created for the rulers to ensure the obedience of the people, but I think a bunch of people sitting near a bonfire telling stories to eachother to give them purpose and guidance in life is closer to the truth (then the rulers discovered that it was a great tool to ensure the obedience of the people).
In my opinion, life would be pretty pointless without a purpose greater than oneself. In the other post you pointed out that a painting would be as meaningful even though there is no point in life. Well if I looked at the painting while having that feeling of "there is no point in life", then I wouldn't perceive any point in that painting either. In fact, the most common feeling of people that are depressed is that there is no point in life, ask them if they would see any point in a painting while feeling that way (I know the feeling, no way can a painting solve that).
I can tell you that there is more than you know, the rainbow doesn't stop where you can't perceive it, it has exotic colours no man has ever seen, likewise existence doesn't end where we fail to measure it, because we are fallible and our instruments are weak. Even so we can already see that a system in the world can give rise to the subjective experience of living, which is already more than can be measured, the system giving rise to the experience can be measured (which is obviously the objective aspect of it), but not the subjective experience itself. Reality have to hold both the subjective and the objective, not only my subjective but all subjective or do you claim that I am the only one subjective? Doesn't all subjectives co-exist?
Again, the brain and the systems within it are only the objective aspect, so if we truly have a subjective (which is self-affirmative) then that is itself indication of a higher existence that we haven't been able to measure, a existence which involves all subjective beings and which contains them.