To illustrate the dilemma at hand graphically, here are pics of two producing shale plays:


Nothing to it - send directional drill down formation, frack stages, extract oil, Bob's Your Uncle.
On a finer scale those formations are as predictable as these simplified renditions make them appear, too. Dust off your copy of Roadside Geology of Texas, the chapters on the Gulf Plains inland from the coast are nothing short of interminable, and as Texans will gladly point out, their state is fricking huge, it's quite a slog to even read about, never mind actually drive through. These are depositional environments that haven't done much of anything tectonically since the Mesozoic - the perfect environment to send a drill down.
Now, the Monterey up close is like this:

This is a land that's chockablock with uplifts, anti/syn clines, innumerable faults, an unceasing barrage of quakes, and more. It'd be a bit of a trick to send your bore down such a twisty bunch of rocks, hence the emphasis on vertical wells and acid fracks. The technological miracle we're presumably waiting for would be a smart bore that could turn on a dime - perhaps literally? Microbores perhaps? Who the hell knows? But for the time being all the oil cos can think of to do is punch holes and burn rocks and see what comes up. Apparently it's paying off a very little bit, but nothing like the copious volumes that would validate the 16 BBO type figures thrown around.
This is all part and parcel of the legacy of CA oil, which is, frankly, crappy stuff. Imagine a slightly more runny version of La Brea and you get an idea of its quality, it's just part of the American legacy that so much attention has been paid to it over the centuries.
Now, admittedly, 8 years ago it didn't look like drillers in TX had done much of anything beyond arresting the stall they were in, and CA doesn't look to be doing anything exciting at the moment either. But still...I'm far more interested in the prospects for tight oil abroad, in northern Mexico, or Russia - or the Paris Basin.