The JWs had taught me that all other religions were false. I realized they were a false religion too. The end.
However, I only gradually came to the realization that I am atheist, about 5 years after quitting the JWs. I hadn't really considered what I believe, but I kept asking questions and figuring things out on my own.
Mainly, though, I just have absolutely no use for religion. These belief systems have been used for millennia to oppress and divide and pillage people, with the never-fulfilled promises of heaven or Everlasting Life™. It's the only con-game where people have to pay, and pay, and pay, (not just money, but time, energy, thoughts, love, friendships, etc.) and never get to enjoy the things they were promised.