This appears as an anamoly now compared to the wide choice of what is available in both revolvers and pistols.
I was in LE during the era this was introduced. If one wanted a compact .45 ACP pistol, it was pretty much a Colt Commander, either stock or very expensively cut down. The Smiths were 9mm. Excellent pistols, but 9mm only because the origin was the Model 39, and later the Model 59.
Revolvers were the predominant LE side arm. S&W pretty much owned the LE market with their K frames. This was considered to be an ideal size/weight for a service revolver for daily carry use. Colt was not competitive in volume with the Smith Model 19 (this was well before the Model 66).
There were jungle drums beating however that the Model 19 did not fare well with a steady diet of .357 magnum ammunition. Bill Ruger saw an opening. The idea was to manufacture a K frame size/weight revolver that could sustain a steady diet of .357 ammo. Given how tradition-bound LE was, Ruger made sure the new revolvers sold at a lower price than their S&W competitors (which Ruger later admitted resulted in the Six series of revolvers never being sold at a profit).
Gradually though the Rugers picked up market share. Gun writers like Massad Ayoob, who freely wrote of the Smith K frame issues, advocated for the greater durability of the Rugers.
In this environment there was interest in a K/Six series sized revolver that could handle .44 spl pressure. ASP, and at least one other custom maker IIRC, introduced K/Six series revolvers with the chambering. The K frame versions did not survive testing, leaving only the Ruger Six based iterations. All this custom work did not come cheaply, so in hindsight it was clear that these revolvers would not succeed in the marketplace.
Despite the insistence of the experts (who still show up hereabouts from time to time) that a cast frame could never compete with a forged frame, the Six Series became acknowledged as stronger than the K frame. This resulted in S&W introducing the L frame series.
This not only resolved the .357 magnum strength question, but now we have the L frame series in .44 magnum. So, full circle and then some.
In retrospect I think a case can be made that Ruger pushed S&W into introducing the L frame to get past the documented deficiencies of the K frames. In so doing they introduced what I have considered from their introduction to be their perfect medium frame revolver.
An interesting foornote in history - this ASP.