Pearce is an extremely busy training base, with the RAAF's 2FTS and 79SQN and the RSAF's 130 Squadron all carrying out continuous circuit training, instrument approach training, departures & arrivals to & from the training areas, together with movements by other visiting military aircraft.
Plus the squadrons of stealth aircraft (and the very occasional PC9 or Hawk) that use the areas of the coast
If PEA was moved a replacement for the LNX areas would have to be found as well. If only PEA and JT were reversed, and PH R24 was long enough for LAHSO.
Actually better yet, if only WA's capital was about halfway up the coast. Hindsight is a powerful planning tool!