In most stories, those with special powers either keep them a secret or are adored by the masses. Clover is different. Those with powers are branded and some are even isolated. In Clover, the cost of being super powerful is living a life devoid of happiness.

Why would the government fear those with powers? Because historically speaking, governments have been afraid of anything which could challenge their power. A person who is powerful enough could easily take over the country and form a sort of dictatorship if they chose to do so. Perhaps Suu would never think to do something like that, but that is not a certainty. Behaviorists argue that all behavior is the result of conditioning. Given the right circumstances, Suu could have been conditioned into an ass-kicking, government toppling, war machine.

Power is a rather funny thing. It is a means to an end at times, but it can also be an end in and of itself. When you have it, it isn't something you want to give up without a fight. Given the right circumstances, it becomes like a drug. Suu and the other Clovers were isolated to make sure that those in power would not lose power.

There is also the mob to think about. How would people have responded to a girl with as much power as Suu? Most likely they would be afraid of her and want her destroyed. Perhaps either Suu or the Wizards understood this and that is why she was isolated.

At any rate, these powers of Suu's came at an unusually high cost, and she never got the chance to use them to fight crime. Instead she lived a good part of her life in a cage isolated away from everyone. Even the other Clover children live with limited freedom, since they are branded, recorded, and tracked by those in power. Still, even this oppressive world allows them moments of happiness.