Why does image generation typically happen through a separate model/API rather than the same chat model producing images inline?

Text generation and image generation are fundamentally different model architectures (autoregressive text transformers vs diffusion-based image models), so 'chat' models that mention generating an image are usually actually calling out to a separate image-generation model under the hood via a tool call — Spring AI's `ImageModel` abstraction reflects that these are genuinely separate capabilities, not one unified model doing everything.