They actually do have that, warm air circulation. The real problem is though that the moisture has to go somewhere for the dishes to actually get dry. It’s why a clothes dryer won’t dry your clothes if the vent is clogged. Some of them have basically something akin to a still inside the door - a path for the warm and moist air to travel through that has a lot of right angle turns giving lots of opportunity for moisture to condense out of the air and then it can drain liquid water out the bottom. Some other models have automatic door openers, so once everything inside gets nice and hot and humid, the door pops open and it all just gets spit out into your kitchen.