Maybe it's just financially impossible for most people to buy 20 boxes of the same cigar at a time.
I think this has a lot to do with it. I wouldn't dream of paying $100 for a 100g tin of pipe tobacco, which equates to 35 or so smokes for me. However, when I was really into cigars, dropping $100 on a box (10-25 smokes worth) would really be considered a mid-range, if not low priced box. Most pipe tobacco tins cost the same as ONE high end stick, and they don't require a humidor that must be maintained carefully, etc.
It seems logical that the fact that pretty much all pipe tobacco comes out of the gate at affordable cost, rather than $200 a box, has a lot to do with the more popular blends scarcity. Many of the limited edition sticks you mention from famous makers, are cost prohibitive for a lot of cigar smokers.
There could be some production related reasons as well, don't know how they compare when it comes to availability of the tobacco itself for the blenders, casing, topping, packaging, etc. Maybe most cigar makers having production/rolling locations right where their product is regionally grown, not to mention cheap labor, makes it easier to ramp up to the demand?
Disclaimer: The above comments are based on no scientific data whatsoever, and are simply the internal half drunk brain dialogue of an amateur pipe smoker who knows next to nothing about the industry. Take that for what it is worth (very little).
sablebrush or one of those dudes probably has a more accurate explanation based on facts and science.