I'm surprised so many older gents had pen knives.
Weight is one reason.
As some get older, weight bugs the fire out of them. Especially those that have knee, back, hip and similar problems.
Another is, these folks know it only takes a small amount of sharp steel to cut.
Oh in younger days, they may have carried stockmans, trappers, and sodbusters, still if one pays attention, they used a "part" of that blade at time.
Heck, often times the blade was sharpened different on one blade alone.
i.e, near the tang, left coarse to cut rope, up near the tip, more sharp for finesse cuts, like skinning, or punching leather
These Elders have earned the right, to not have to wag around a heavier knife, and with years and years of experience, they know how to use a little bit of sharp steel.
Arthritis "sometimes" means, holding things different, ink pens, coffee cups, and with a smaller pen blade, not being "heavy" or "long" they can use the palm of the hand.
The knife "rolls" in the hand, if you will, as they knife is an extension of them.
Now many will go to a small fixed blade, like a wooden handled "whittler's " knife.
That wooden handle can be shaped to fit them, and the blades (most often carbon steel) are only 1" to no more than 1 3/4" long.
Danged arthritis kicks in, and getting an nail into a nail nick, and the resistance of a back spring is "onerous".
Just easier to pull a small fixed blade to handle tasks and slip back in a nice sheath.
Safer too, in not having to un-fold/ fold a knife.
Locking knives, means even more exposure of fingers and hands to edge.
These Elders have always known, just sometimes the young bunch ain't ready to be receptive on what all, is what all, and why.