I wouldn't call myself as particular on train maintenance...but consider that these trains are run more or less continuously. You thrash your car in seasonally tough conditions every morning, but these drive all day and most of the night. So, I'm not sure if the comparison is apt on these grounds.

A cursory search suggests that quite a few manufacturers design for light rail car lifetimes of 25-30 years, not forty. These tend to be of European origin, which tracks San Francisco switching from an Italian to a German vendor. I don't see evidence that it's a common practice to significantly extend the tenure of those devices there nor here.

Funnily enough, I see no problems with the Breda trains personally as a passenger. But once they've shaken out the major bugs, the Siemens train reliability is anticipated to be triple or more. It may not make sense to design a traincar for a fifty year term.