Most likely it's because people sometimes call Guzzi's "Tractors" - for example Greg Bender's very good Guzzi site [You must be registered and logged in to see this link.]
The whole knobby tires thing is very hot with the custom bike crowd right now - they are rapidly gaining on the Firestone Deluxe Champions as the hottest poor tire choice. Plus street trackers and 70s scrambler style bikes are now more highly regarded by the hipsters than cafe racers. The mini non-functional "fender" on the front pretty much confirms this was built for someone who values form over function. I'm guessing the owner puts less than 500 miles on it and then sells it to "fund another project",
All that snakiness aside, I think it looks pretty good - but better with tires without so much sidewall.