Don't know if its true about a lack of instructors but Darwin has for quite a long time only had the one flying school in operation, and whilst it has always been busy enough for one full time instructor, there have been extended periods where there just wasn't enough flying for a second (especially given the low demand due high prices). My understanding is also that Darwin Flying School has recently been sold off so it wouldn't surprise me if there was some regulatory / operational reason why flying school ops aren't taking place.