They chose which style they liked best. A few eventually ended up in Open and WFTF..... The rest preferred Hunter.
When I got started in 2007 there was only OPEN division. Since then I've shot an equal amount of time in both Hunter and Open and this year I've been challenging myself with WFTF. It's an interesting comparison. Physically its easier to adapt to Hunter style but with the equipment limitations of 12x its actually more difficult on the scoreboard. So I don't consider Hunter as a "beginner" class. It's just a good format to get started in because you don't need customized rifle stocks, with specialized equipment like the adjustable knee shelves, butt hooks etc... to compensate for the ergonomics of sitting on the ground/bumbag.
In HUNTER, All you need is a bipod, a stool, 12x scope on top of a Sporter style air rifle and your in the game.
"It doesn't get done til someone does it"