Why Isn’t Proposition 22 a Slam Dunk with Voters?

I thought voters would find a "yes" vote for Proposition 22 to be an easy decision.

The proposition would end Sacramento's ability to decide that it's in a crisis and needs to raid taxes dedicated to transit funding (as well as other local public services, such as the police and fire departments) leading to the massive service cuts that we've seen locally and across the state. Not surprisingly, transit advocacy groups such as the California Transit Association have donated hundreds of thousands of dollars to see the initiative pass, and local groups such as the Southern California Transit Advocates have made passage a top electoral priority.

Yet, newspapers from Los Angeles to San Francisco to Sacramento are lining up against the ballot measure. Los Angeles Mayor Antonio Villaraigosa hasn't quite declared opposition, but has repeated the basic argument against the measure:

In other words, because the state has been raiding locally collected and dedicated tax funds for so long, putting the money back where it was originally dedicated would damage the state's general fund.

Most of the arguments are a variation of this theme. Teachers unions complain it would balance the budget "on the backs of students" while the "vote no" argument in the official voter guide argues that passage "eave us all in greater danger from fires, earthquakes, floods, and other natural disasters. It also means cuts in emergency medical services, forcing longer response times if your family needs a paramedic—or perhaps no paramedic at all in a major emergency."