Why are people presenting the false dilemma of having either no cellular service or station/service interruptions?
"Protesters" have zero right to vandalize websites or physical property, steal personally identifying information, or cause service disruptions. They should expect to be caught when CCTV and cell records are subpoenaed & should look forward to felony conspiracy charges.
These demonstrators were doubly stupid because they alienated people who agreed with them. The transit union and mayor came out against the cell shutdown, as did many riders. Why infuriate those who agree with you? But just because the messengers are in the wrong does not mean their message is.
BART is not a private company that can do whatever they please. The California Public Utilities Commission regulates BART, and BART is partially funded by taxes. The public (and the transit union) have been supportive of cell phone coverage due to the safety benefits they bring (this was particularly true after people learned of the cell use during 9/11). I'm unconvinced that cell shutdowns disrupt protesters so much that it is worth losing this piece of mind. Any communications disruption has real financial costs & nobody has shown the math that shows those costs were lower than alternative actions that could have been taken.
BART receives $6.7M a year in telecommunications revenue ($2M from cell service). You take that away because you cut service & you have to make it up some how. That'd be a 2% fare hike (not including FCC-imposed penalties or fees for breaching the telecom contracts).