My theory is that they are only around to stop us from detonating nuclear bombs. Why? I am not sure. Maybe they want the energy for themselves. Maybe the detonation attracts unwanted attention from elsewhere in the universe. Maybe the detonations interfere with their technology. Why hide from us? Probably because we would end up hurting ourselves with the technology that they have. Imagine if most people on the planet had something that could be repurposed as something that acts like a nuclear bomb.