ChatGPT was the starting gun for many AI founders. Prior to ChatGPT (and right before that Midjourney and Stable Diffusion) most people in tech were not paying close attention to the Transformer/Diffusion model revolution and dislocation we are now experiencing.
This means that people closest to the model and technology - ie AI researchers and infra engineers - were the first people to leave to start new companies based on this technology. The people farther away from the core model world - many product engineers, designers, and PMs, did not become aware of how important AI is until now.