Do any Bay Area folks understand the system for waiting in line to board a BART train?

This has always struck me as very odd. In the downtown San Francisco stations, especially heading towards the East Bay at rush hour, people form lines on the platform and wait there. Then when a train comes, it’s only the right train for a few people, so everyone who wants to get in just ignores the line and walks in the doors. Waiting in line doesn’t seem to actually give anyone an advantage to getting in sooner or picking a better seat. Has anyone else noticed this phenomenon, and is there a point to the lines that people form? Am I missing something, or is it an excercise in futility?