I suspect that the change over from the kilt as common, everyday clothing to less commonly worn ceremonial garb may have played a role, as well.

When you are wearing the kilt simply as your clothing, the lower yardage kilt makes a lot more sense, both in terms of economy as well as practicality and comfort.

However, when a garment is used for more ceremonial purposes, it tends to become more stylized and exaggerated. Let's fact it, all that extra cloth in the kilt lends quite a bit to the swish and swing of it! And when you are trying to make a kilt from a greater amount of cloth, knife pleating is definitely easier than box pleating.

So as the nineteenth century rolled on, and less and less Highland men were wearing the kilt as their daily garb, reserving the kilt for special occasions (if they wore it at all), there may have been a trend for the kilts to contain more fabric, which could have then contributed to the popularity of the knife pleated kilt.

This is purely speculation on my part. Really, do we know why any fashion changes the way it does? :-)