Why do my flights always use runway 24L at LAX airport?
Two words: sample size. Eventually, you will use another one :)

There are only 4 runways, and they are all used heavily.

LAX normally has a westerly traffic flow, with aircraft landing/taking off toward the ocean.

How the airport operates:


  At all times, the inboard runways shall be preferred to the outboard 
  runways for departures


and


  well over 90% of all operations use the preferred runways


Quotes from this document. Nice graphics can be found in there, too.