because they're inoffensive for now
Let start winning against NA/EU teams...
A lot of the interest in Japan stems from their completely unexpected interest in the game itself. This is the first fps game that the Japanese fanbase watches for the competition. While their performances are undoubtedly lackluster even in comparison to other minor regions, the fact that they were even able to bring some form of competition at the highest level impressed many. Being offensive, if anything, would really only serve to further increase the "love" for Japan. Brazil and SEA both have had experience, interest, and participation in major FPS titles, which is why they feel less "loved" - they're just not new to fps.
However, with immense investment, support, and a thriving player base Japan will almost certainly improve. I hope that organizations choose to develop homegrown talent than always relying on imported players, though.