ISO 16154 specifies tractor lighting requirements.  Although it is an International Standard, not every country has adapted it but in Europe it is demanded.  Depending on cost, companies may build to the standard for all nations they supply just to make assembly, quality control, and part number control easier.  Others may be country specific.  The lighting standard is 41 pages and I no longer have free access.  It is likely the answer is there - the Korean tractors with brake lights may have them because it is a European requirement and they may not differentiate between American (US & Canada) and European.  Kubota, however, assembles their SCUTs for North America in Georgia so they would likely not have brake lights.  They go by ASAE B279 which does not require brake lights.  And by the way, another thread talks about high mounted warning flashers on Kubota Grand L cabs getting knocked off.  The standard requires 2 amber flashers 3.3 to 12 feet above ground so removing the cab top flashers and using only the fender mounts meets the law.