Hasbro covered that in the Round Table. They saw how crazy sales were on the blue shirts and regreted they couldn't resupply fast enough to fill the need. This being DTC, they have much better control over that.
A few things to note: Those are replicas of the vintage thighs, but it's still the BAT feet, and modified BAT waist (it has the ribbing on the side, but still no ass). Plus, one of the Steel Brigade is based on the winner of the Maxim "become a GI Joe figure" from last year.