Question

why do people horticulturalists , florist benefit from the black rose

Answer 1

The Black rose is a symbol for death, as opposed to the red rose, a symbol for love. Generally, the black rose holds the same mysterious romance held by the red rose, but in a much grimmer sense. Florists benefit by selling it, and the other two by using it for symbolism at any event and engineering how to make them easily.

Answer 2

all of the above, plus for the challenge, pushing boundaries.
whether by genetic manipulation or with special growing techniques of florists.