The problem with finding new venues, is you need suitable trails where you can get landowners permission to use them, and infrastructure.
If you could guarantee dry weather, there are plenty places that could be used. However taking Aberfoyle as an example, some of those trails would simply be destroyed after a couple hundred riders in the wet, and even in the dry you’d have to make some tough track choices if you didn’t want to attempt to damage/scare too many riders.
Then you have infrastructure. Go somewhere where there’s no reasonably sized town nearby, then you’ve got accommodation problems. Not everybody wants to camp, or is willing to drive over an hour to get there each day. That’s before you take into the things like ambulance availability, or general supplies.