Why does it keep happening? Because of LAX security. Sorry that was a bad pun, I will now dodge tomatoes.
LAX is the only airport in the united states that has recently been a known terrorist target. Muslim terrorists had plans to blow this up, complete with extensive floor plans. So if anyplace should take security seriously, it is LAX. I think they do have more security than other airports, but it is still disturbing to see this kind of repeated slip. Hope they catch the guy who dodged security.