Nobody said that 21 million bitcoin is enough for us, because the truth is, every bitcoin users around the world desires to have more bitcoin as many as possible, because this is our true nature, we want more as long as it benefits us. And not all the people around the world wants bitcoin and know about bitcoin so this 21 million bitcoin is too much for all the bitcoin users right now, if all the people around the world will use it, then it is not enough.