The following is my own theory(ies) for the 'humped' lanes:

1) The method in which the threaded needle pierces the material to attach the short string of 8-12 beads, and the desire to keep a design that will adequately cover the project, would inherently lead to the arching of the strand. The hump could be avoided by the extra time consuming use of a second thread to hold down the strand at one or two places, similar to two-needle applique. Is this where the coined term of 'lazy stitch' may have evolved?

2) Prior to the introduction of the glass bead, decoration was done with strips (lanes) of quillwork. Did this carry over to the beading methods?

Again, my theories...

"We do not inherit the Earth from our ancestors,
we borrow it from our children."