Well yeah, when there's never any cops to kick off the homeless insane, people are going to prefer the privacy of their own car.
IOW, the flow of benefits from hiring more police officers goes in directions that make it politically difficult or impossible to get the additional money. And you need a lot of it.
Though adding officers would benefit rider safety and increase the quality and pleasantness of the rider's experience, the increased taxes would fall mostly on people who do not use the system much or at all. (To raise fares would discourage ridership.)
And police officers aren't cheap - each one costs about $150,000 per year (according to a 2011 article which estimates that adding 725 officers to the LAPD added 110 million dollars a year in costs. [0])
[0] http://articles.latimes.com/2011/nov/22/opinion/la-oe-ridgew...
Public transit will never be a profitable enterprise. It must be subsidized. But we already subsidize roads for cars, but somehow the car-lovers just ignore that.
that's probably true overall, but it matters where the benefits flow to and where the taxes flow from.
in LA, how are we going to increase taxes on car travel enough to reduce car trips to the point where deaths and pollution are noticeably reduced and then redirect those new tax revenues to improving public transport? what politician or government leader can deliver that message and actually succeed?
one of the first political realities that leader will discover is that the increased taxes must not be levied on working poor drivers. (most of them still need to drive their cars because public transport is not everywhere yet.) there will be a lot of complaints. and such taxes could actually increase levels of poverty because some poor workers won't be able to get to their jobs in their cars anymore. such a leader would be demonized for hurting low income people.
that means the leader will have to propose an even greater tax hike on the middle and upper classes. well that's a hard fight too. those people vote. they fund campaigns. they also do not use the public transport systems as much as other income groups.
So basically, there's no realistic solution at all, and that society is headed for an inevitable collapse because of its own shortsightedness.
Every nation gets the government it deserves, and this case is no different.
the existing local political processes seem insufficient. i've seen it play out this way for a long time.
but i believe an externally imposed shock (e.g. oil rising to $5000/barrel or a deep local economic depression) might accomplish what local politics cannot