I don't understand why atheists deny the existence of a creator.
Because there's no evidence of one. And generally I don't go around believing in the existence of things for which there is no evidence. But like all conclusions from data, I'm tentative about that.
God
could exist, I guess. There's nothing that, to my knowledge, prevents the existence of God. It's just my conclusion from the data that he doesn't exist at this time. So, given that there's no evidence, I'm absolutely sure that god doesn't exist - but I know I could be wrong.
When i look to logical arguments, although i don't think they are a proof, it seems to me that the arguments that say that nature as a rational structure, structured by a creator, are better when compared to what atheism has to say...
Nature doesn't really have that much rational structure. Unless you'd care to explain why I possess an appendix with no specific function.