To attract their 'own' pollinators.
Almost all flowers that emit a scent are pollinated by insects.
It is beneficial for plants that pollinators, after visiting one of them, head to another similar flower. This ensures that the pollen of their own species reaches the flowers, rather than that of another species.
For this, flowers have characteristics that help insects recognize them: shape, color, and, of course, scent. Its composition may include substances that are attractive to the 'right' pollinators.
