Healthcare has its own problems, but the 12 hour shift model was adopted because it improved patient outcomes. Only having 1 shift change per day provided less opportunity for patient context to get lost in the shuffle. In short, overworked doctors/nurses were better (for patients) than uninformed doctors/nurses.

Moving to 6 hour shifts/4 changes per day would quadruple that risk.

Now, there are plenty of ways to imagine changing procedures, policies, and tooling to reduce this risk, but it would require planning.