I dunno, I think to far too much an extent it is about followers of fashion, when I was a nipper Ray Mears was not even born, and my first "bushcraft" knife (I don't think there was such a thing as bushcraft then) was a six inch bladed sheffield bowie. I don't think there was much choice then because that is all there was. Blades were on the large side and clip pointed.
My current user at least has the distinction to be Finnish, but it still has a 5 inch blade. It's the handle I do not like though because it is rubber and not very bushcrafty at all. For all that the blade is not over large and the extra length can sometimes have it's advantages when you use it as a draw knife.
Five inches is a happy medium I think, neither too large nor too small, and I don't give a monkeys if Ray Mears gives it his approval or not.