My newbish thoughts are that this likely has something to do with the consistency of how the filler is put together. Since the filler is a mix of three leaves from a tobacco plant, top / middle / bottom.
Without to much detail the three leaves are picked seperately as they have different flavor profiles and consistencies based on how much sun they got, the top being thicker and richer for example.
Often they have a formula for how much of this how much of that goes in when they make these fillers, however cigar flavors can change as the amount of each leaf changes through the length of the smoke.
I may be way wrong on this but hopefully someone more experienced can chime in and add to this discussion or set my newb head on my shoulders straight.