BART exists in 5 counties (San Francisco, San Mateo, Alameda, Contra Costa, and Santa Clara) and multiple cities (SF, Oakland, San Jose, and multiple smaller ones).
Having people who have jurisdiction in any bart station is useful. And for example, consistent foot patrols are valuable to BART but not necessarily valuable to the city of Hayward, or whatever. As a concrete example, BART has more or less a goal to be able to put an officer on the car within a stop or two if you report on the app. That's logistically challenging for like a half dozen reasons if the bart police wasn't it's own org.
Having people who have jurisdiction in any bart station is useful. And for example, consistent foot patrols are valuable to BART but not necessarily valuable to the city of Hayward, or whatever. As a concrete example, BART has more or less a goal to be able to put an officer on the car within a stop or two if you report on the app. That's logistically challenging for like a half dozen reasons if the bart police wasn't it's own org.