Rules and regulations in aviation are written in blood. Moving fast is not a virtue when the industry is already as safe as it is. Even if the change is to something objectively better with no drawbacks, the act of change itself creates risk for accidents.

Basically when accident rates are already very low, even a small amount of transitional risk can add up to offset years of marginal improvements. So the burden of proof rests heavily on the proposer of change to a system that already is working reliably.