Yeah, but why Monday-Wednesday-Friday only? The plane appears to be sitting around on the other days.
It's not as if I can't invent reasons why they chose to do it. The extra flight is just odd because it's not United's style. For all of the other flights that do not fly every weekday, it's because the plane is being used elsewhere or because only a single aircraft is dedicated to the route and the plane can't complete a turn in 24 hrs.