I rode Test Track without a fast pass and I didn't even wait an hour. I went to Epcot when it first opened. What I do is get fast pass for Soarin first and head to Test Track. Soarin is longest wait for a Epcot attraction. People usually head to soarin' first for getting in line or for a fast pass.
The 2 hour wait is likely caused by breaking down. In front of me in line for Test track last year, I saw a car break down. The other reason for the wait could be weather related since a part of the ride is outside.
The popularity of Test Track is easy to figure out there. There is a Racing crowd that goes to WDW aka F1 fans, NASCAR, Indy CAR, drag Racing and other forms of racing. The 2nd thing is Future World has issues for attractions. Journey into Immigration with Figment is not exactly popular. Wonders of Life no longer having attraction don't help.
World Showcase is better known for its shopping, entertainment, and food than rides.