Traction engines were not the first engines on the farm: prior to that, you could find steam engines on wheels that would be pulled by horses to different areas of the farm and fields to run belt-driven machines such as bailers or threshers, which were stationary -- you'd load hay into a baler with a pitchfork, and the machine would compact it into a bale.
Tractors absorbed this function with their own belt wheels or the PTO on modern tractors, which is used to power machines stationary or moving (modern bailers move around the field, but tractors will still be used to power a stationary grain elevator). They also added three point hitches and hydraulics to automatically raise and lower equipment.
But as long as it pulls, it's a tractor.