Because there was an overnight stop in LA. The flight from Toronto doesn't arrive in time to catch the flights to Hawaii; thus the luggage couldn't be checked through.

Also, I was not taking the next flight in the morning (it was too early). So its apparently classed as a stopover, not a connection. The agent said the problem was actually the ticketing done by the AA phone rep; if it had been ticketed on one ticket (which it should have been) instead of two it would have been OK.