TL;DR: Religion is a part of human nature; personal greed, and wars and such are also a part of human nature. Unless human nature can be changed through some means, either supernatural, or through trans-humanism, there's not much you or anyone's Utopian ideas of what one key change could be made to alter human nature can do about it.
How can people, in general, be religious? People are generally predisposed towards religion. When you happen across isolated, tribal folk, you generally find that they're religious. Since all people were once isolated, tribal folk, that whole "religion" thing has kinda stuck. People, as a whole, are generally fond of religion, except for those who have "hating/disliking religion" as part of their religious beliefs (like OP). Perhaps because the secular religions aren't super big on proselytizing, excluding the New Atheist movement, or maybe because Secular Humanism is a harder sell than Evangelical Christianity when you're dying of various diseases in some small village somewhere, that the secular religions haven't taken over the world yet.
If some sort of apocalyptic event happened, the current religions of the world might disappear, but new religions would eventually take their place. That's just the way people are. The question is, is this inherent religiosity a bad thing? I, of course, would say no. People divide themselves from each other for all kinds of reasons. No elimination of religion, or establishment of a singular religion over the entire world would make people stop fighting each other. If all but one particular ethnic group, sharing a language, religion, and general culture remained, eventually they would start fighting over resources, perhaps justifying it because the enemy sat on the wrong side of the campfire, or whatever.
That's just the way people are, unless you believe that human nature can change, either through supernatural redemption (or other similar religious/philosophical principle) or through some kinda trans-humanistic techno-wizardry.
As for why I'm personally religious, not that anyone cares by this point, it involves finding a satisfactory purpose in life, not just for myself, but for the human race as a whole. My previous religious beliefs, after I decided Buddhism was more negative towards the physical world than I discovered I was, was that the attainment of knowledge was the highest good there is. "Good" was defined as that which facilitated the attainment and spread of knowledge, and "evil" was the opposite idea. I pondered several times what this means in the long term. In this hypothetical history, where everything progressed according to that principle, first there would be the abolition of independent nations. I once thought that the very idea of having separate countries was the "big bad terrible thing" that was ruining humanity. "If only folks could all just join together as one, that would just be swell.", I thought. This unified Earth would set aside all differences and get down to researching everything that is, eventually getting to space travel, and uploading the entire human race into a unified consciousness. I wasn't, and I'm still not, a big fan of individualism. "If only folks could stop all their petty working for themselves, and instead join together to learn about everything that is, that would be grand." I thought. The united Earth consciousness would spread throughout the Universe absorbing, and collecting the information of any encountered life. Eventually the consciousness extends across all the Universe, so the whole Universe is working as one to learn all there is to know about everything ever. Given an infinite amount of time, the consciousness learns everything, and compiles a Universal Encyclopedia. And then what? Having learned how to create life, should the consciousness create more life, and thus more things to record? It could theoretically do this forever, constantly learning new things (the consciousness figured out entropy and all that). The important question is, "Why?" What good is pursuing knowledge for knowledge's sake? I think Futurama covered something like this once, it was a What-if episode where science has finally discovered the principle of life/the universal equation/whatever and there's nothing left to discover.
The above is essentially a super-long way to say that, without any sort of external source, human life is devoid of an overall purpose. The response to this being religion. Like it or not, at some point you decided for yourself that humanity's purpose is to "put their footprint on this very large universe".