A seedless watermelon is a sterile hybrid which is created by crossing male pollen for a watermelon, containing 22 chromosomes per cell, with a female watermelon flower with 44 chromosomes per cell.
Just a little to technical for me but that was the answer when I looked it up.
I prefer melons and fruits with seeds. I think they are much more flavorful and as a kid we had the added fun of flipping the seeds at one another.
They did the same thing with roses. They managed to create great big long stemmed roses and sacrificed the scent of the smaller varieties.