Why are flowers pretty? They ride first class with us and push our buttons.

Playing twenty questions as kids, we were allowed "animal, vegetable or mineral?"   I was superior to humble plants.  They however are more like us than you may think and represent the most recent and innovative development of a billion years evolution.  They are so advanced in fact that they recruit almost every creature in the animal kingdom to help reproduce.  They craft their lures to attract the hairy bee legs that collect pollen, they add hooks to piggy back on mammalian fur,  tobacco and poppies concoct addictive drugs for homo sapiens, sugars and bright colours capture the attention not just of humming birds but of the crown of creation, our very own humble selves.   All that without wings or legs or a cerebrum.

They immodestly decorate their genitals to be sure that highly-evolved brainy creatures stop by to investigate and help make plant sex successful by transporting DNA.  Perfume, nectar and eye-catching colour are popular  lures.  They are attractive because trial and error has found the buttons that move us. An ivory tower philosopher may wonder if beauty is universal.
The garden variety thinker sees that whatever gives an organism a future (life and progeny) is hardwired to create a pleasurable motivating sensation to seek it out.   The flowering plants skillfully take advantage of this, because they are riding in the same first class coach as us, they know us, and are the product of a school of hard knocks in which they learned a thing or two.
The principle is delegate to others what you don't need to do yourself.