It's not a quick desicion, and it may not be a choice and individual response as much as you might think. Religions have been around for ages, humans as a species, even more. However, both he capability of self examination, and the possibilities and interest to research and discover our past and tracing our evolution in terms of culture, tendencies and thoughts, how our thoughts relate to the world and how we came upon those thoughts, are relatively recent. When doing this we started (I say 'we' as a whole, we humans) to notice repeated patterns with variations throught history and the world. Inside this patterns were beliefs systems, and each of them we've found them to be wrong to our point of view (I'm talking about really ancient cultures), so we can come to the conclussion, or assume with a logical response, without exploring and investigating EVERY single religion that exists or existed, that the trend of believing in and worshipping deities is false from the premise; so whatever variations, details and whatnot that might derive from that false premise will be incorrect or at most incomplete.
Furthermore, this question applies to anyone who even choses a particular religion to begin with. If you want to know what makes someone reject every religion, you could look into and ask yourself why haven't you researched, explored and came up with at least one reason why not to follow any religion that you don't follow, from the present or the past.
Personally, the main reason I don't like religion is that each one says "we're correct and this is THE truth", while science explores and concludes "this is more likely than this or that", and art doesn't even pretend to be true in the first place.