Sometimes the tracks get seized up from rust. Especially when sitting in the dirt for a long time. My 22 had rusted up tracks and I would go out every day and spray a little diesel fuel in the links with a weed sprayer. I would try pulling it around every week and it finally broke loose.
By the look of were it sits it might be the tracks or the brake bands might be stuck I had that problem on a D2. Take a hammer and see if the tracks move up and down between the idler and the sprocket, that might let you see if they are stuck.
Try hooking a chain to the top of the track just in front of the drive sproket and pulling on one side at a time.