Here are two reasons I think you don't see many charter airlines in the U.S.
1) Americans don't really go for package tours, especially within the U.S. Probably because it's easy enough to plan your own vacation, and you can get just about anywhere by scheduled airline or car.
2) Charter airlines work when there are large numbers of leisure travellers all going to the same place at the same time, to areas that don't have enough scheduled service to meet the tourist demand. Americans don't all go to one vacation spot, so it's hard to support tourist-only flights. Even the old "vacation" airlines, like Sun Country and ATA, wound up going to scheduled service. Europeans seem to be much more homogenous in their vacation plans. In the U.S. you do see charter flights to high tourist areas, such as Hawaii, Florida, and Mexico, but overall, I think it's more common for tour companies to book seats on scheduled flights.