The problem was not so much conservatism of gun owners, but that the Dardick was a complex solution in search of a non-existent problem, built partly on a piece of deception.
The deception (or maybe self-deception by Dardick) was that if you made the cases triangular, you would get more rounds in a magazine than if the cases were round. But a little thought shows that to be false. A "tround" at best will fill in the gaps left by round cases, but the number of cases of a given caliber in a given size magazine will not increase. In fact, it might decline, depending on the thickness of the case wall, which, because of the gaps in the firing chamber, has to withstand pressure a conventional case wall does not.
The use of the "revolver" cylinder really contibuted no advantage, and had all the disadvantages (barrel-cylinder gap, timing) of a conventional revolver. Dardick touted the fact that the gun was "double action" but even then there were DA auto pistols on the market, handier and less bulky than the Dardick gun; the new breed of pistol (e.g., the Glock) with the same or higher cartridge capacity put the kibosh on the Dardick idea for good.