I'm seeing it in my area too.
There was a time 20 years ago when you could have your pick of boarding spots. I remember when I was looking for a new boarding barn and I had 10 barns written down to pick from - all within 20 minutes or so and trail riding available right off the farm.
Now, I struggle to find one that I can afford that has just a small area to ride off of the farm. Now, all of the farms are listed as "boutique" or cater strictly to eventing or hunter/jumper. I think the trail rider is becoming obsolete. At least in my area. And as more of us age out of it, I think it's going to go away completely at some point in the future. As farms get sold, they also close the trails that were on those properties.