... does anyone know why JLC chose not to carry on the bridge detailing of the 40s into the 50s and beyond?
There is a hint of times past on the Cal815&25 main bridge, but think how pretty a Memovox Cal489 might be with Geneva stripes and gilt finish comparable to a 45x/46x... or a fully-finished Futurematic 497.
It depends which movement really. Higher end movements like the Breguet hairspring moonphase movement are decorated. Probably costs really, after world war II, most of Europe was broke and the U.S. market kept the Swiss alive.