Except you do, because otherwise your belief is logically incoherent.
Explain.
This is a really big claim, you have to follow it up with something.
If you analyze each religion, many core traits are shared. Most religions have underworlds and heavens as well as a supreme being along with gods, demigods, or heroes who taught humans certain skills, moral codes of conduct, veneration of ancestors, rites of passage, an afterlife, impermeable forces (i.e. mana, sin). That's just the cultural universals, there's other beliefs like reincarnation which are widespread but not universal.
Most religions?
Are you including the thousands of them that didn't get widespread and got lost to time or regional ones?
Or just the big ones that got adopted by empires and spread through conquest?
Saying "I don't believe in any gods" is akin to saying "I don't believe the sun is yellow." It's on you to propose how "nothing created everything" (the default atheist, otherwise you're just spouting pure nonsense.
That makes no sense.
I don't have to have any explanations since I'm not making claims, I'm just rejecting claims.
I'm not proposing any system in place of a theistic one, I'm just saying I'm not convinced by it.
It's up to the theists to provide evidence of their extraordinary claims.
This is an old theistic tactic of shifting the burden of proof, I've seen it many times before.
And that's not even getting into the philosophical challenges of atheist morality, another reason why there are (almost) no real atheists. Atheism is inherently amoral (since with nothing to establish a moral code, you have no reason to not steal, rape, and kill to your hearts content), which is why atheists need to either borrow civilizational (i.e. Christian or Jewish) morality or devise their own religions like Science Worship (Darwinism, since evolution gives a moral code), communism, libertarianism (i.e. Objectivism), or environmentalism.
I can easily make a case for those being something you avoid.
I don't want to have my stuff stolen, nobody I've ever met wants their stuff stolen, therefore it's safe to assume people in general don't want their stuff stolen.
I don't want to be raped, nobody I've ever met wants to be raped, therefore it's safe to assume that people in general don't want to be raped.
I don't want to be killed, nobody I've ever met wants to be killed, therefore it's safe to assume people in general don't want to be killed.
See? I don't need an old book to tell me those things are wrong, I can just figure it out from looking at the world around me.
Are you saying that if an old book didn't tell you that theft, rape and murder are wrong... you would perform those acts?
Who is the amoral one here?
If one truly just believes that a religion is false you're simply a non believer. Most likely non religious.
To state you know for certain no god exists, that requires some degree of faith.
Well, that's what the A in Atheist stands for.
Atheist means non-theist.
To call yourself an atheist, adopt atheist symbols, beliefs and causes. Well now it's starting to become a religion.
What atheist symbols?
Some person somewhere made some symbols and established some causes but that means precisely jack shit to most atheists.
They have conventions, everytime some christian tries to have an afterschool activity or group activity sanctioned by the state atheists demand they to get to prostelytise as well. They form internet communities and mock religions so they can socialize with other true believers.
Who's they?
You seem to think atheists are a monolith.... they're not.
Those conventions and everything else you've mentioned, only a very small minority of atheists participates in that.