What do you think that LLMs can do exactly? Sometimes naive technologists think of AI as some sort of magic solution. But if you look at overall healthcare system costs, very little is being spent in areas that could be easily automated with an LLM.
And for T1D specifically it would be very dangerous to put an LLM in control of something like an insulin pump considering that we don't have any way to do quality assurance to the level required. Simple, deterministic algorithms are preferred for safety critical systems because they're less likely to fail in bizarre or unpredictable ways.