Well I would guess Gravity capped it at 50% for it to take longer for players to level a guild. The longer it takes, more likely the more money they will make in the process as well.
Now why it isn't 100% on heRO...no clue. Guess we've just been used to the "status quo". I personally think something in the 70-80% range is more than enough, but if 100% is an option as well, I wouldn't be against it.
