Meant for a Greater Potential

As the younger sibling, there was a possibility that Hanabi would be placed in the Branch Family and receive a cursed seal, once the next heir had turned three. However, because her father felt that Hanabi was a more suitable heiress than Hinata, and because there have been several changes in the way the Hyūga family works, she became exempt from this. 

Since she is a girl, however, it is also possible she was never meant to have a cursed seal in the first place, as Japanese tradition usually only allows men to start a branch family.