Atom bombs have extreme explosions, but they also require extreme maintenance, extreme precision in manufacturing, and are extremely detectable.
For AI the level of extremeness has not been defined. Yea, it requires extreme manufacturing, but it's the same manufacturing that builds billions of chips per year that are distributed almost everywhere. A server farm running AI looks much the same as a server farm running other computing tasks.
Coming back to atom bombs, yes, atom bombs could destroy the world 10 minutes from now, and every 10 minutes from now until we destroy enough of them they can no longer do that. It simply has not happened yet and we've likely been very very lucky that it has not happened.
Lastly, AI, especially when we reach AGI, is intelligence which means it will likely have some hand in if the world is destroyed or not. This risk rapidly increases if AGI capabilities are far beyond human capabilities.