In 2008, Hillary won a very close race in Indiana, receiving 646,235 votes to then candidate Barack Obama's 632,061. Of course, Obama opened up campaign offices there in February, long before the primary was even on the radar, closely followed by Clinton. Both candidates ended up visiting the state numerous times. This was very different than the strategy Bernie used this primary cycle.
I'm not saying he has any chance, but, he has the capacity to go on a spree in May leading to CA in June. Discounting that reality has kept Hillary's voters on the sidelines. Hillary and Bernie voters in the remaining states need to participate in this process and vote.
However, the California primary has funky rules. If you're a registered Republican, you can only vote in the Republican primary. The Democrat primary is open to any other registered voters. When people feel empowered, they will be more likely to go out and vote. This is crucial for both Bernie and Hillary supporters in the remaining states.