"There are quite a few reasons off the top of my head. One being that Colts were not commonly in that caliber"
Total production numbers of .44-40 v/s .45 Colt SAA's "thru 1910" anyone? 1910 picked as that was likely towards the end of use of these as a primary means of defense and utility, so a comparison of production numbers in that time period would be educational. Then a look within the subset of .45 Colts to see the percentage sold to civilians v/s the percentage sold to the military. My bet is that total sales to civilians favored the .44-40.