I’m an atheist because it is a rational intellectual stance about a proposition for which there is no evidence and no rational justification.
A personal god – as I presume theists believe – has never been observed in the history of humanity. It is, strictly speaking, imaginary. God can only be imagined, not observed, therefore belief in such a proposition has no base from which to operate. It does not add to my understanding of the world. It does not help me deal with immediate emotional, familial, social, professional or avocational problems that I might encounter. It unnecessarily complicates any system in which it is introduced. It is not needed. It is not plausible.
There are a nearly unlimited number of tangible and plausible concerns about which I can attend. God is not part of them.