I would answer more but I'm kinda stuck on them.... Well besides
Flowers celebrate valentines day because of the meanings behind the flowers. Each flower you give means something different and is like giving candy heart messages. For example a pink carnation means gratitude while a white one means remember acne or a forget-me-not means remember me forever while lavender means distrust. You can find more meanings here. But that is why flowers celebrate valentines day, the meanings behind each one.