So, like the Bar exam is really hard, it's just a ton of horrible memorization. That's awful, but hey you do it once when you graduate and you get certified and I could be okay with that.
But that's not it. If you move (to a state without reciprocity, or without practicing long enough, both of which happen often) - you have to pass again in your new state. There are some exceptions where you can be an assistant with an out of state bar and so on, but basically you have to pass again.
So you've been a practicing lawyer for 10 years or something, you decide you want to move to CA, and now you have to pass the bar. Surely your practice has been in some little specialty, so it's not like you remember all the other weird details of all the various laws outside your specialty, so you have to study all over, and it's *worse* - it's the worst kind of new test, because it's really similar to what you studied before, but just very slightly different.