LAX doesn't have as many slots as ORD or ATL in reality, it's got about 1/3rd less slots in real-life, but it should have more than it does in-game.
A while back I provided sami a list of all major US airports (top 25 I think) and what their slots should be per the FAA. Because, for the longest time, all US airports were identical in size in AWS except ATL, MDW, and JFK. Some of the most egregiously incorrect were updated for these latest games (starting with North America Challenge), but not all of them. LAX is one of them that hasn't been. Even the ones that have been adjusted weren't made exactly right, but they were adjusted so that the were more-or-less proportionally correct. So rather than moving them all up, he adjusted the really big ones up so that they were at least proportionally larger than the others.
So, while LAX is still too small, it's at least proportionally correct to most other airports. i.e. it's roughly the same size as BOS, IAH, or MCO as it should be. It's about 1/3rd smaller than ORD as it shoudl be. And it's got about half the slots in-game as DFW as it should. ATL kind of throws it off though, as it's correct in number, but proportionally off other US airports since almost all of the others need to be adjusted upwards a good 30% or so; it should have been adjusted downwards from previous games to be about the same size as ORD (actually a tad less) but it's higher number of slots was retained when the adjustments were made.