As BART’s ridership surged three years ago, along with the number of homeless people lingering inside its downtown San Francisco stations, the transit system doubled down on custodial work — and some of its janitors started cleaning up paywise. One system service worker, BART’s title for janitors, made a little more than $271,000 in 2015, with $162,050 of that in overtime. A year later, two other BART janitors joined him in collecting more than $100,000 in overtime pay in a year. Three years later — after the tale of the high-earning BART janitor became legend and the transit system, and...