The answer is almost always personal support / personal assistants.

There are for sure ways to increase your own personal productivity on its own, but the extra kick is usually from in-house cooks, cleaners, shoppers, schedulers, stylists, PAs, etc.

These people may or may not be spouses, family, friends and so on.

(This is a general response, I do not know Simon Willison or any of his work or life.)