I think it is very apropos that the future site of the stadium sits on a polluted toxic landfill. A nice home for two sh*tty teams.
1) Divided loyalties - Go to any Dodger, Angel, Laker or Kings game and observe the high number of fans rooting for the visiting team.
2) Distractions - There are so many other things to do, that pro sports are too far down the list.
3) Fair weather fan base - When LA teams are winning, that team is the hottest ticket in town, when they are losing, stadiums are half full.
The above points do not even include how the LA Coliseum Commission (in the past) screwed the pooch by losing: Lakers, Kings, Rams, Raiders, UCLA (Football) and USC (Basketball).
BTW: I was born in LA, left when I was 39 years old and have attended games at every venue and for every team mentioned above (except for the Kings). I saw the Dodgers at the Coliseum and the Lakers at the Sports Arena.