Lots of reasons:
- Smaller trees than out west
- Small bars (and smaller saws) are lighter. We don't have the monster trees you have out west, so the need for greater length for felling and bucking is far less. Why carry around that extra weight if you don't have to? 20+ years ago, that was not as much of an issue for me as it is these days. (Though an old college wrestling injury to my neck and upper back has always been bothered by long days of chainsaw use.)
- The shorter bars make a better match for the power required to cut dense hardwoods. The vast majority of what I cut works just fine with a good pro-level 60cc saw and a 16 or 20" bar. If I'm doing more than just an occasional cut in someting bigger, I might bring a bigger saw.
- More easily maneuverable: When limbing the trees I deal with, a long bar just gets in the way more often than not.
- I'm almost never walking on top of the tree while limbing. I understand that is more common out your way. If I were, a longer bar might make more sense to me. I walk on the ground beside the tree. limbs are generally within easy reach. If I'm doing a lot of limbing and bucking (such as when cutting up firewood), I'll drop a tree crossways to the others first to set up a bench to hold the next ones to come down at a convenient height. I'm also relatively short (5' 8"). Standing on the ground next to a tree, a long bar would require me to reach out with it to cut, rather than working with gravity and reaching straighter down.
- It's poor body mechanics to reach out to cut with the end of a long bar: you are working at the wrong end of a long lever. A longer bar just tempts me to push this even further (and sometimes requires me to work further out on the bar, since there is no room to get the powerhead close to the cut for some limbs when the tree is on the ground). The longer the bar, the more strain you are putting on a wide range of muscles to cut out at the end of it. (I my case, it also means getting another lecture from my physical therapist wife when I ask her to fix me after straining something).
- I try NOT to bend my back to get low. That's another example of poor body mechanics. I use my legs to lower myself. (... or risk another lecture and my wife getting fed up and sending me to the chiropractor, rather than fixing me herself.) Having tried both ways, I find this is easier on my back than a day of reaching out with a longer bar.
When I was younger and in better shape, I could just bull through a lot more than I can these days. These days, I find I can get more done and over a longer period of time by using good body mechanics and using the lightest equipment appropriate for the job. I'll admit that my opinion on exactly what is the "lightest equipment appropriate for the job" has changed over the years.
I'm not trying to say that my way is the right way or the best way. It's just what works best for me in the type of woods where I find myself working. I'm sure that if I were working in similar conditions on similar-sized trees as you (and were as young as you), my methods would probably more closely resemble yours. You have obviously spent some time learning your craft and adapting your techniques and your equipment to what works for you and in the conditions in your area.