I worked for United for 5 1/2 years. There’s a rule about checking bags – if the layover is more than four hours, you’re supposed to collect, then recheck your bags. There is some leeway on this, but for the most part, sounds like they’re trying to enforce it.
An airline’s baggage room sets-up containers, or carts, for flights, so as the bags come down the conveyor, they can be placed in the correct flight’s train. If your flight is eight hours down the road, then your bag just has to sit there, and wait till its train is ready to be filled.
What else do you you have to do in LA? Go to the beach??? 😉