Well in context of recent attendance, 23 & 20 doesn't seem that different - ~10% less is a pretty good drop-off rate for 10x the distance from Perth.
The events that stand out from the last two years, other than the state champs, are the urban MTBOs:
38 @ Bayswater
30 @ Glen Forrest
47 @ Bibra Lake
34 @ Point Walter
So....oh wait, it's the same conundrum as foot O. Do we compromise "true" orienteering to get attendance, or try to run the events the die-hards want even though attendance continues to drop. Your problem is that you're starting from a much lower base.
What's the point?
You keep asking that question, and yet you (personally) keep driving MTBO in this state. So presumably it's worth it to you, I'm guessing because it's the only way you get 'race' practice?