What you are missing is that there are two type of coefficients of friction, static and kinetic. For a given material, the coefficient of static friction is higher than the coefficient of kinetic friction. That means that there is more friction when the items in question are not moving in relation to each other. If the tires lock up in a skid, you are dealing with kinetic friction. If the tires continue to turn, but just barely at the level of losing traction, then you are dealing with static friction. This means that you will stop faster in that case. This is exactly what anti-lock brakes do by preventing the wheels from locking up and skidding.
It is like when you try to push a heavy box across the floor. It is harder to get it moving than to keep it moving.
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