I, too, think it had a lot to do with both the traditional looks and traditional shooting styles. Up into the 60s, police officers in many jurisdictions earned their "marksman" and "expert" shooting badges shooting one-handed, single-action, at ring targets.
And both the Centennial and the Bodyguard had an issue with being non-traditional: With the 49 it was the humpback appearance, which only a mother could love; I must admit it took me a while to warm up to my 649, although I think it's the most versatile subcompact handgun ever. And on the original Centennial, even though its appearance was a lot more streamlined, I've been told the grip safety turned off a lot of potential customers because it appeared as an awkward and superfluous appendage.
It is worth noting that the competition, i.e. Colt, as far as I know never felt motivated to experiment with versions like that of its .38 Spl. snubbies, although there was that odd-looking aftermarket hammer shroud you could install on regular exposed-hammer Detective Specials.