Not only software, but pixel art is free to create (MS Paint can do it), you have control of exactly each pixel placed.
Pixel art is an expensive "art style" and many people will pay just to get that retro style (ie Scott Pilgrim, The Hunger Games, Megaman 9)
Problem with pixel art is you can't do zooming in and out with them which is vector art's advantage (perhaps ONLY advantage) over pixel art.