Besides popularity and trends as an issue, how many people buy a second touring bike or upgrade touring bikes? A mountain biker may go from a $400 hardtail to an $1000 hard tail to a front suspension to a full suspension bike. A roadie may go from an aluminum bike to a aluminum carbon mix to all carbon fiber. Once you buy a touring bike, you're pretty well set. People ride a touring frame forever, and short of buying a different brand, you can't buy a higher end tourer through most. Components may change, but how different is today's 520/T800/T2000 from the same ones made a decade ago?
When I was shopping a few years back, the local Trek dealer told me to make the 4 hour round trip drive to the Trek Store in Wisconsin to try it and then come back and he'd order it.
I more or less stumbled into another shop out of town that had a T2000, in my size no less, sitting on the floor. Wasn't there to look for a tourer, but it caught my eye. Granted it had sat there for two years, but that's how I found mine.