Studying music is not all about fun. In order to be the complete musician, a pianist has to pass through the challenging studying process: practicing, concert, and EXAMS. Talking about out of the comfort zone. When I was little, I used to think that the piano exam is like the most 'evil' thing in the world. The idea of repeating and practicing the same pieces for 8 months, just makes me tired and hate music.
The piano exam is definitely not an absolute parameter of a successful pianist. Even though my student got perfect score for music theory and piano practical, doesn't mean that they love what they're doing. But piano exams are, or could be, a useful tool to compare one's technical level or factual knowledge of piano and music to some objective standard - and thus could be helpful in countries which do not have a long established western musical tradition.