Atheism is a belief; it establishes a single absolute conclusion to the same question.
Agnosticism is not a belief; There is no conclusion drawn because of a lack of supporting evidence. When god can be proven or dis-proven mathematically or personally then a decision will be made.
Other religions are beliefs; drawing absolute conclusions without verifiable explanations.
The difference between atheism and agnosticism is artificial and of recent origin.
Most people who are not religious now, are not religious for the same reason: There is no proof that a god is required for the universe to exist.
Any reasoning person, when shown incontrovertible evidence of something, must come to accept that same something. It's how science works.
Show me simple, repeatable and verifiable proof that god exists, and I'll be a believer.
I wouldn't consider the difference between Atheism and Agnosticism artificial.
It's the difference between "I don't believe in God" and "I don't know if God exists, or in what manner or form God may or may not exist."
I view it as the difference between choosing an answer and searching for an answer... This isn't a time sensitive question where the lack of an answer counts as a "no."