Hello Thomas,
Its quite simple, it requires more skill to forge the metal to 1/4".
The Kami in Nepal do not have very sophisticated equipment and to ensure good lines on that stock requries more time and a better eye.
Most kami are only caple of making tourist kukri, which are of rubbish standard. It has been very frustrating finding good kami, I am lucky in having good and patient friends help me out in Nepal.
Please remember that in the past most military issue were made in India and a lot of the best early kukri were also made there. After WWII there was not a big call in Nepal for exporting kukri, it is a fairly recent demand for good quality kukri. As a consequence they are having in many ways to re-learn their craft still and over the last four years I have seen a big improvement, as well as some right bosh jobs along the way.
Having said all that they are getting better and better and more able to cope with the high standards required in the West.