Automatics also allow for engine braking. From a quick search, it sounds like a toss-up as to whether that triggers brake lights. Regardless, the article mentions the benefit is not only from cars slowing down, but also from indicating that a car is preparing to stop or “that a stationary vehicle might initiate movement”. Neither of those can be done by an engine brake, so front brake lights would still have a benefit even with a driver that likes engine braking.