Climbing up the pole to get to it would be what would keep me from doing that. The actual zipline looks like a lot of fun!
I get in a panic with any mountain roads that don't have some sort of barrier on the shoulder. It could be as simple as a rock but it's
just enough to give me the illusion of thinking I couldn't go over the edge. My SO took me on a car trip on a back road up from the base of Canyonlands to Dead Horse Point, UT (IIRC) that had me nearly in tears because most of it had no barriers on the shoulder and the drop off was to my right. I had to keep my eyes closed going through a lot of the Cascade Mountains traveling east on I-90 (Snoqualmie Pass area, etc.) for the same reason. You couldn't pay me enough to do that walk out over the Grand Canyon even though you're enclosed. I did mostly okay at the South Rim, though, because of the railings and being on solid ground. One lookout did have my knees shaking and I had to step back from the railing.