The simplest field analysis for the performance engineer is the balanced field case where acc/stop = acc/go. Ignoring a few complicating factors, there is only one set of conditions under which balanced field = actual field. All other flyable scenarios are conservative. So providing data for balanced fields is (for the pilot user) simple and conservative. Also the flying techniques are unchanging.
Hence, it is often possible, at light weight/cool day/good headwind combinations, to actually be able to find a theoretical V1 at or even above Vr.