I am an unconventional non-believer, certainly in the context of this forum, and I recognise that a lot of the people who hold themselves to the label "atheist" don't have a very strong basis to it, not unlike many "theists" (in fact, in my experience, extreme theists who loose their faith tend to become extreme atheists, and vice-versa while moderates generally remain moderate regardless of how their core beliefs evolve).
And excellent observation.
I have often noted , too, how, among theists, the gods they 'worship' tend to very much resemble themselves in spirit ad temperament. Angry men worship angry gods. Greedy men worship greedy gods. Frightened men worship abusive gods. Kind men worship benevolent gods. And so on. The lesson being that most people choose the gods that confirm their own natures and desires, not the gods that challenge their natures or desires. Ot's not always the case, but often.
I'm not sure what you present is quite how it works though. A monotheistic religion (which will be pretty much all we're talking about here) will present the ideas that A) Some kind of god exists and B) This is what that god is like. If you loose faith in that religion, you loose faith in both assertions.
Yes, that often happens. But I'm pointing out that it's not logical. And if we take a moment to consider it, we will see why.
Religions don't assert that "A" God exists. They assert that THEIR God exists. That God as God is depicted via their theological reality exists. And that's to be expected because that's the purpose of religion: to help the adherents stay their particula chosen theological course. But when one of them decides to reject that theology, and it's depiction of God, they have no logical basis upon which to be rejecting all theologies and all theological depictions of god, and even less of a logical basis to be rejecting the god proposition en total.
And yet this is nearly ALWAYS the case, and always the claim. There is no law that says humans can't be irrational. But too often these particular humans are telling us all about how exceptionally logical and rational they are, and what critical thinkers they are. And it's just not the case in this instance.
It is certainly possible to consider other religions or philosophies that state the same point A but a different point B, but in the absence of any such idea being presented, weak atheism would be the default position.
No version of atheism is a "default position" because the default position is no position. And atheism is not "no position'. It is the antithetical position. No position is the state of mind that exists prior to and/or apart from the theist proposition. Unaffected and undetermined.
The other aspect is that many of these religions share very similar (and sometimes literally the same) support for the existence and nature of god, and so they fall foul of the same challenges. Once a person has countered the ideas of one monotheistic religion, an alternative one would have to do something more and different to convince them.
It doesn't matter because religions are not theism. And theism is not religious. And atheism is a particular philosophical response to theism, not a response to religion. And until people get this strait in their minds, and stop confusing and conflating them, they will remain confused and illogical and irrational, despite their constant claims to the contrary.
Being bitten by one dog certainly isn't a valid reason to hate all dogs, but it'd be natural and reasonable to be more cautious around unfamiliar dogs than the average person would be, and certainly more than the average dog owner.
We humans are not logical beings. So what we deem to be "natural" behavior is often still not logical behavior. And that's to be expected. But let's not let this becomes and excuse to mislabel or misrepresent or disparage of be dishonest about and through our irrationality. By all means be an atheist. But please be as honest an atheist as you can be. That's all I'm really proposing. And I would certainly propose the same to theist.