With regard to the CA bar specifically, it has one of the lowest pass rates primarily because it permits anyone to sit for the bar irrespective of whether or not they graduated from an ABA accredited law school. Most other states, by contrast, only allow ABA grads to sit for their respective bar exams. When you compare ABA stats to ABA stats, it becomes apparent that California is not the "hardest bar exam in the country" that most think it is.
Take look at the statistics available on Calbar's site. Non-ABA grads made up a whopping 6% of first time test takers last February. If every single non-ABA grad failed, the effect would only be 6%.
Fully accredited ABA schools from out of state often have pass rates in CA that are 20-30%, even though their in state pass rates are 80-90%. The fact that CA has a tougher than usual bar exam is evidenced not by the handful of non-ABA grads who fail, but by the thousands and thousands of fully accredited ABA grads who fail.
I wouldn't use data from the February exam as the standard for bar passage in any state because the February exam is typically comprised of repeat takers who were unsuccessful during the July exam. Studies show that your chances of passing actually diminish after your first attempt, thus the February passage rates in most any state, including California, will historically be lower for February than they are for July.
That said, many claim that the California bar exam is the most difficult based on its July passage rate which, for ALL takers is usually around 55%. However, "ALL" takers literally means everyone, including the repeat takers who, as discussed above, typically do not do well on their subsequent attempts. When you look at only the first-time takers of the CA bar exam, the bar passage rate is actually 68%. When we look at first-time takers from CA's ABA schools, that number jumps up to a 79% pass rate. As far as bar exams go, a 79% pass rate is actually pretty high.http://www.protectconsumerjustice.org/california-bar-exam-pass-rates-by-law-school.htmlhttp://abovethelaw.com/2011/01/california-bar-exam-results-open-thread/
For an apples to apples comparison, the bar passage rate for first-time takers at New York's ABA accredited law schools hovers around 85%. That's only a 6 point difference between the two states.
You said that:
"Fully accredited ABA schools from out of state often have pass rates in CA that are 20-30%"
That's actually not true. For the July 2013 California Bar Exam, the bar passage rate for ABA schools from out of state was 64.2% (906 out of 1,411 out of state students passed). That same stat for July 2012 was 63.6% (907 out of 1,425). In other words, the majority
of out of state students at ABA schools pass the California bar exam.
That's not to take away from the difficulty of the California bar exam. It is, without question, one of the most difficult bar exams in the country. However, people should understand that it's not much worse than other states when you look at ABA schools (which is what most of us have attended, are attending, or will attend).