I do not fully understand the reason but the way it was explained to me goes something like this since led bulbs do not have the same resistance as a normal resistive bulb the ecub thinks the bulb is still on for some reason and remains energized as a result

Heres what youre not being told

If your vehicle has a softoff fade to black lighting system that is controlled by the ecub electronic control unit body it is likely these bulbs may cause a parasitic drain problem to your vehicle battery