twists
Yes, I would certainly agree that Ruger would take any step that would economize production and yield some increase in profit. The new .44 carbine line was likely dropped because of low sales and lack of sufficient profit.
But I would hope that Ruger had reconsidered their twist rate selection from 1961. As noted the slow twist rates were standard at the time for various manufacturers carbines and I suspect harken clear back to the .44-40 in the early Winchesters. Ruger had introduced the Super Blackhawk in '59 (before the carbine) and could have applied the logic of same twist rates for both at that time, but did not. Carbine twists were slow, and I suspect that the logic was accepted and the Ruger went ahead with its 1:38. In that same era, the 240-250 gr bullet was pretty much industry standard.
By 1996. with the introduction of the 96/99 series there was an interest in shooting heavier bullets from the .44 mag. Hornady had its 265 grain bullet available, and I think Speer offered a 300 gr number, I think with two cannelures two allow for carbine and revolver, and there may have been others. There were articles written about shooting very large game with cast lead bullets weighing in excess of 300 gr. The slow twisted carbines did not shoot those slugs well. (I suspect the really long slugs may not have cycled thru the actions, but that's another matter) . My thought is that Ruger considered these trends when selecting twist rates for the new carbines.
Contemporary .44 lever carbine producers seem to have recognized the need to tighten up. I read Henry started out with 1-38 but are now 1-20. Since Henry does not produce revolvers, this seems an obvious nod towards improving accuracy with heavier bullets. Rossi carbines I read are 1-30, some improvement from the traditional rate as well. Chiappa is twisted faster as well.
Why did Ruger do it in 1996 and continue (we hope) with the Marlin 94 if they get around to it. I guess we'll never know for sure.....may well be for both reasons, accuracy and economy.