Whatever the details, knife handles SHOULD, first and foremost, be designed to fit the human hand....and not just in one way of gripping it, but in every way you can image. To that end, here are what I consider "hard and fast" rules of knife handles, and the reason(s).....
First, look at the human hand, and how it closes around any object grasped..... the smallest area of the "grip" is where the thumb and index finger come together.... and the largest/most open area of the grip is the heel/pinky finger area of the hand. This means that a knife handle should be smaller/narrower in the front, and larger/wider/taller at the rear of the handle. From there a maker can do any number of things, but, no matter what else or how else you do anything to a knife handle, if you fail to follow the basic "smaller in the front and larger in the back" rule, the handle simply will not "fit" well, nor does it feel "right".
The single biggest mistake I see in newer makers is handle design/creation. Many tend to make the rear of a handle small and narrow, and the front large and wide. Another thing that should always be in a makers mind is sharp angles/edges.....neither have any place on a knife handle.
This is way over simplifying it, but if you can whittle a 2x4 in half with a given knife, and not have blisters in the end....you've produced a "comfortable" knife handle.
As to the original question..... Various knives, particularly
factory/production knives have handles that are designed in favor of ease of production rather than comfort of the end user. That means IF a maker looks to production/factory knives for handle design input/inspiration....it's very likely you shouldn't be, and it will generally guide you down the wrong path.
This often bleeds over to new makers, because they do not have any other example(s) to follow, nor do they yet posses enough knowledge to understand applying ergonomics to knife handles. In fact I know of a number of "custom" knifemakers, who have been at it a LONG time, and still haven't figured out how to produce a comfortable/user friendly knife handle.
One HUGE REASON that we see a lot of poorly made/uncomfortable knife handles these days is due to many using CAD software to design knives....again, particularly newer makers. That's because the newer makers still don't have enough experience to understand the ergonomics of a knife handle, but also because CAD software lends itself to angles more than curves. Again, don't get me wrong, CAD has it's place and so do "patterns", but as with anything, when they are relied on too much, or exclusively, they become a hindrance, rather then an asset.