Too much of a hassle is probably the main reason. Ate Typ 200 is the exact same fluid, just amber like pretty much every other brake fluid. The effort or hassle of trying to source it is more work than just running more fluid through the lines. The perk of super blue was the convenience of monitoring color when alternating from super blue to typ 200 every change, so you knew when all of the old fluid was removed. Realistically, running about 90% of the can of Typ 200 will get most, if not all the old fluid out of the system.