
Sakura's bad luck makes much more sense in the context of the curse. It wasn't because SHE was unlucky; Saga's curse prevented her from succeeding and pursuing her dreams.
She herself would have saved Saga, and the universe set out to ensure that didn't happen. And after trying and failing several times to discourage Sakura, only for her to still not give up, it was finally decided that the only way to stop her would be to kill her.
Essentially, it turned Sakura into its own personal cosmic toy so that she would never achieve anything in life before finally deciding to drive her into a car accident.