There are thousands of religions, and many philosophical explanations for who we are and why we are here. Some are similar, others diametrically opposed. One thing they have in common is none of them are certain, and if one believes in any of them, it requires faith.
Faith, defined: "strong belief...based on spiritual apprehension rather than proof."
Right there in the definition of faith, we see it requires a lack of proof. If there is proof, it's not faith, it's just observation. Here we have reason #1. No proof. The rebuttal to anyone saying there IS proof: If there is proof, then it is not faith. If it's not faith, then it's not a religion. If you are trying to say your religion has proof, then by the very definition of religion and faith, you are delusional.
Next reason: Improbability.
Out of these thousands of options with their creative explanations of life, it's very unlikely that any one you choose or that appeals to you is the right one.
Even if hundreds of millions of others believe the same thing. Example: Hinduism vs. Judaism. "1,200,000,000 people can't be wrong", is the argument I've heard. Well, yes, actually, they can. Either that, or over 2,000,000,000 people who believe those people are wrong, are wrong. Having numbers doesn't make you right, and is listed as one of the logical fallacies. See "Argumentum ad pupolum" : https://en.wikipedia.org/wiki/Argumentum_ad_populum
Given this information, the only logical solution is to just admit you don't know. It's not that hard, it doesn't hurt (unless you are really egotistical/narcissistic, etc). It's just the truth. You don't know. No one does. There are those who think or believe they know, for whatever reasons (fear of the unknown, false confidence, upbringing, lack of intelligence, inability to accept reality, etc), but simply by accepting that you don't know, you put yourself a step ahead of the fools.
Just those two logical foundations alone are enough to dissuade anyone of sufficient cognitive ability to fully understand them from subscribing to or continuing to participate in any current world religion. Not that everyone has that level of cognition, or ability to extricate themselves from their subjective reality enough to observe the information with an unbiased and logical mind.