It is pretty unusual for a 2-WD tractor not to have "loaded" rear tires for traction purposes.
Today, very, very few tractors under 5,000 pounds bare weight are sold without 4-WD.
In 5,000 pound tractors the exception are "haying" tractors which operate on level fields, usually without an FEL, powering hay balers. A limited volume category but a category not ignored by tractor manufacturers.