Short answer: because flowers are pretty.
Apparently flowers really wanted to earn their reputation for being symbols of peace and love, because basically all fangirls can agree: flower crowns are adorable.Fanlore
Pretty mundane, right?
Then it got weird(er).
In 2013 it was the Hannibal fandom's time to shine.
flower crowns seem incongruous in the context of cannibalism and murder
Because flowers and murder go together like salt and pepper (?!)
"This is my design..."
(◡‿◡✿) (ʘ‿ʘ✿) “what you say ‘bout me” (ʘ‿ʘ)ノ✿ “hold my flower”
✿＼(｡-_-｡) “Kick his ass, baby. I got yo flower.