No, it's a fair question. Since the bike in question is a SS cruiser, it probably has a narrow OLD, horizontal drop outs with no derailleur hanger and a coaster brake. None of these are insurmountable, but all these features would cause extra work if converting to a derailleur.

Oh, traditional derailleur? I suppose there have been cruiser bikes with derailleurs back to the late 50s or early 60s, but, and its a big but, cruisers with derailleurs have never been that big an item. There were many IGH cruisers prior, and it's still common enough to this day.

BTW, speaking of traditions, when the French cyclists were trying to work out acceptable, robust, marketable derailleur gearing in the 1920s, German and British cyclists had been riding really excelent IGHs for a quarter century.

tcs