They even make semi-auto dirt bikes now, the small ones for kids.
If you come from the M/C world, manual trannies are still the way to go, and appreciated for the control you have with the hand clutch, esp at take-off.  It is hard for dirt bike riders to make the transition to quads, whether sporty or utility.
There is no question that CVT-auto ATVs are the most popular, and for good reason.  They work, and are easy for anyone to use.  They are reliable as well.  Torque-converter autos (Honda) are pretty slick, but rare and expensive.  You can still buy the ubiquitous Honda Rancher 420 with semi-auto, as well as full-auto.  The former costs a little less, but I expect it to go away eventually.  Auto is king.
A quick check shows that some majors have already dumped the last of their manuals and semi-autos:  Polaris and Arctic Cat (Textron).