yes, inside the FE mathematical engine 1D elements are constant stress, so you could plot element stresses and see the step change. But this is unrealistic, and people prefer continuous plots. continuous stress plots map stress from element centroid to element centroid (or node average to node average) and so there is a smooth variation along the length ... it looks more natural.
"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.