Given the MTP drafter is basically a separate model, keeping it separate makes more sense IMO. It's out of my wheelhouse but it seems like you could adjust the MTP drafter model separately from the main model, too.

Ultimately though the real explanation, I think, is Google doesn't care since for their own purposes (in LiteRT-LM), they do bundle them. As far as I know, anyway.

MTP models share internal state with the main model, and also refer to parameters in the model.

They are more like a single model that has two separate attention head mechanisms.

I mean just like GGUFs aren't technically necessary yet are _way_ more convenient than using Safetensors and configuring the default Jinja prompt by-hand, it makes sense to bundle the draft model too. For all intents and purposes, the only people who will train a draft model are the people who train the original model