Channel 39 wasn't an option because 3ABN got a permit in 2010 to construct a 15 kW station located at a site near Hayfield on that channel. The 3ABN station on channel 38 near Rochester interferes with this permit, but as owner of both stations, 3ABN was willing to accept that.
Whether the channel 39 permit will get built has to be in doubt at this point. 3ABN applied to move the station to a site 7 miles to the north in part to lower their tower rent, but the FCC dismissed the application for being too close to the Minneapolis-St. Paul market. Now, with WEAU back on channel 38, the proposed station has the problem of causing interference to the WEAU signal.