As well as making the lamp that it doesn't mind the polarity, it could also be to allow for AC supplies if the light is run from an alternator that produces AC.
It may not be done any more, but some lighting driven from small engines, like pull-start outboards, lawnmowers and kick-start motorbikes is driven directly from the alternator coils on AC. It's still common on the generators on bicycles, so the LED bike lights designed to run from them will have the bridge rectifier, even though some will be run from battery packs.
The empty capacitor pad may show that the manufacturers don't think it's needed any more. You may get some flicker with AC if the capacitor is missing.
It's certainly better for the manufacturer of the light include the diodes than to require the customer to wire the light one way, or to have really bad light flicker when connected to an AC supply.