"Man you caught me there. For some reason, its one of those things that I have to really think about."
I started using seatbelts religiously when I was autocrossing. Of course, usage was mandatory...but I also found trying to stay in one place in the seat (even with high bolster buckets) was extremely distracting when cooking back country roads. Seatbelt usage became habitual quickly...
On the tractors, I feel very uncomfortable without using the belt. And, of course, not using one makes the ROPS not only useless, but dangerous!