Paul, I don't think it was because it was cheaper! There were tons of lobby cards printed in Italy for English movies from the late 1950s to the 1970s, and also they did lots of special color sets for U.S. movies (from 8x10 to 11x14 to 16x20), PLUS there were some larger special posters.
ALL of these had much superior quality of printing and color to that of the U.S. or English printers of those times, so I suspect they went to Italy for the superior printing rather than lower cost.