For international arrivals, most bags get x-rayed for nasty contents (mostly looking for drugs) before they appear on the reclaim belts (I am not referring to the customs x-ray when you leave the arrivals hall where they are primarily looking for food type items). They bags may also be sniffed by dogs and may even be swabbed for chemical trace analysis. This all takes time, and the time it takes depends on how thorough customs is being for that specific flights, and that may vary depending on their intelligence (no jokes intended), flight origin etc.

For domestic flights, the bags just need to be retrieved and delivered to the correct belt. The Australian baggage handlers have learned from their US colleagues that providing poor service is a self-defeating exercise. They have seen US travellers willing to check less and less baggage due to the very poor service and long delays, resulting in the need for less handlers.

The Aussie handlers have realised that if they deliver a good service, passengers will be very willing to check their bags and hence their jobs will be more secure.