There is a big difference between van-supported and self-contained touring.
I would think that ACA - fka Bikecentennial - would see the importance of maintaining a self-contained Trans-Am.
I got my start on ACA's self-contained Northern Tier group trip in '99. It was a game changer for me, especially since I had never toured self-contained or camped a night in my life.
I suspect demand was the main driver of the decision. As a NFP, it's tough to run a trip that loses money because of a lack of demand.
Assuming a drop in demand is correct, what is the cause?
Aging demographic?
Upfront investment in touring specific gear? That 4P tent someone has in their garage isn't going to be useful for a self-contained tour.
Time constraints for those in the workforce. We work longer hours with less time off.
General financial conditions of potential participants? When I did my trip, only 2 of us were in our 30s. Everyone else was 55 or older (6 people, and only one of them was in their 50s and still in the workforce. The other 5 were 60 or older and retired.) or 25 or younger (4 people). With cutthroat competition the way it is, how many recent grads have the time and money to take off a summer to ride bikes. As for retirees, the average American has relatively little saved for retirement, and pensions are rarer and rarer these days. A three-month, self-contained tour is not cheap, especially with what some places are charging for camping. I forget exactly how much I paid in '99, but I am sure it was over $2,000 way back then. Might have even been close to $3,000. And I had to buy an appropriate bike and all my sleeping gear and foul weather riding clothes. (ACA supplied the cooking gear.) I also had to get myself from the east coast out to Seattle. (I rode home from ME after the tour ended.)
The proliferation of e-bikes pushing some towards the paths of least resistance? (
E.g., The Katy Trail on an e-bike sounds like a lot more fun than pedaling up mountains.
Interestingly, this year was Cyle Oregon's final week-long event. (Fully supported camping) I believe it was their 36th year. (I did the 25th edition in 2012, among others.) There were lots of reasons, but I believe demand and the ability to earn a decent ROI were two of them. I think the plan is to have shorter duration events.