A number of factors can be involved. The jet stream can change, or flow control from air traffic control could require that the flight enters the approach through a different "gate" in the sky. Being that this flight was delayed, this could be the case in order that planes are sequenced to land with the least amount of delay.
Local report here from LAX is that AeroMexico officials say that flight may not go tonight either.
Flight 225 is now over New Jersey.