This is related to tales I'm literally in the process of writing, tales related to Resurrection, so read at your own risk. But you asked fun questions, and I want to answer them.
So:
The Bloom can't be simply used to rewrite reality. It's not a creative tool like that, one you can just … use to make what you want happen.
The Bloom rewinds the timeline and "resets" it. After this, the timeline can unfold differently. Not necessarily better. (Though it does at least temporarily fix 'reality breaks' if such things are present.) And there will always, always be effects of the prior timeline… or, well, prior timelines.
I wonder why the Bloom was so horrible.
Because the Bloom can't simply be just… used. It has requirements for its activation to become available. The requirements are different in each timeline (hey, it's a psychic plant growing on the universe, it's… weird). If you don't cause the timeline to meet the Bloom's current requirements, you can't use the Bloom.
The Bloom's requirements are the problem.