There is still unfortunately a large jump in price from a good wetsuit to a dry. Add in the maintenance required on a dry suit (undergarments, seals, zipper, hole patching) and it becomes a significant barrier for some (including myself right now).
It is rather easy to bulk up the thickness of neoprene to handle 50F water in a 300-400 dollar 7 or 8mm suit. With a true semi-dry, you might gain another 5F (45F) for another 200-300 premium.
It is not nearly the same gain you get from going dry. What the numbers hide though is the comfort on subsequent dives of the day. Wet, these can be miserable below 50F and dry they are comfortable. Even more of a difference on the SI when the outside air is cold and windy, I have frozen my butt off sitting around in a wetsuit for a hour long SI.