Those guns are desireable NOW because they are out of production and collectibles. When they were being made, not enough people wanted them and those who did didn't want to pay the price that would have had to be charged to make a profit. And if Colt brought them back today, exactly as they were, and sold them at a competitive price, no one would want them because they are an obsolete design. And if they brought them back and charged enough to make a profit, the guns would cost $1500 apiece and no one would buy them.
As for bringing out a new design that could be produced and sold at a good price, they tried that; Colt fans slammed them for copying S&W and stayed away in droves.
Art buyers know all about the "death dividend." An artist's work goes begging until he dies, then it becomes collectible and the prices skyrocket.