Wasn't always the case. The IS200 sport, GS sport etc. were designed and modified in Europe/UK from Toyota TTE and other European sourced parts (O.Z. wheels) - Lexus GB would order a standard GS300 for example and replace suspension, wheels, and body parts on import to convert it to a GS300 sport. That all stopped when TTE/Toyota Motorsport GmbH turned into the Formula 1 team.
Back then, Lexus didn't exist in Japan and Lexus models had the Toyota badge, with TRD developing performance parts for them. The F division occurred very soon after Lexus launched in Japan, in part because they can't really use the TRD name on a Lexus, even though TRD as still producing the parts, and also in part to compete with AMG, M division, RS in the US - Europe has never really been a consideration for Lexus designers except for the CT.