hamon

That makes sense, the hardened edge on a kukri should be narrow to provide a hard edge only, since the cutting targets of a kukri are things like solid trees, which would damage a sword, you'd need a large shock absorbing body. Having a brittle edge extending far into the main body of a chopping instrument used on hard materials would seem counter-productive.

Good point too about 'unintentional' hamons, the 'art sword' crowd miss the point of what swords actually are, tools for combat, and they similarly forget what differentially hardened edges are for, which is to create a harder cutting edge for efficient cutting and edge retention, not to make pretty patterns.

Considering that the Japanese couldn't even work out how to forge steel, and were taught how to by the Chinese, and considering that they were also taught by the Chinese how to differentially harden blades, it's laughable how differential hardening is spoken about from the perspective of the Japanese, when they were one of the last nations to catch on historically and all they did is make a fuss about it when they learned how to do it properly. It's like discussing a topic from the least significant perspective really...

From sevenstarstrading.com/site/2010/10/myths-about-chinese-swordsmanship/

"A method of heat treating used to produce blades with hard edges and
softer, more resilient backs or centers was the differential hardening of
a blade edge by using refractory clay mixtures. This technique (popularly
known as clay tempering), made famous by Japanese sword smiths, originated
in China in the early Tang dynasty (seventh century AD). This method was
adapted by the Japanese during the Tang dynasty (618-907 AD).
This differential hardening method involves using the refractory clay to
insulate the back of the blade (thus changing the rate at which the steel
cools), while exposing the edge during the quenching and hardening process.
The radical temperature change at the edge produces a thorough crystallization
of the carbon in the steel to make a hard edge while keeping the rest of
the blade from becoming brittle. When done properly, this method produces
a very hard cutting edge backed by a softer blade body, which retains the
resilience to absorb shock. Though some Chinese sword smiths continued to
use this refractory clay method well into the nineteenth century, it generally
fell out of use by the Song dynasty (960-1280 AD). Henceforth, other methods
of hardening were adopted, possibly due to Central Asian and Middle Eastern
influences during the Yuan dynasty."

The Chinese were more concerned with performance than looks and didn't polish with stones to show the temper lines.

It's important for people to keep Japanese history in perspective rather make assumptions based on baseless romanticism that samurai strutted the battlefields with 'beautiful swords'. The Japanese originally produced straight temper lines but only very much later by the twelfth century Japanese smiths started producing irregular temper lines for decorative purposes.