...but, perhaps they had a reason to be downtown?...or in the urban area? ...whereas, if they were in a rush, as most people who are stealing a truck would be, they would take the 403, take the Oak Park exit to a known dumpster.. and get onto the back roads as soon as they could...So, IMO if they were in fact seen downtown, there was a reason they had to go that route.
As repugnant as it may be, try thinking like the perp in deciding what your route would be.
A potential reason is the 403 is a much busier roadway than Wilson/Colborne at that time of night on a weekday. If you're DM, the last thing you want is a trucker peering down from a high up vantage point into the vehicle and seeing either TB being restrained or perhaps already dead at that point.
The Wilson route into Brantford also offers the availability of quiet side roads where DM and accomplices could have had privacy to either subdue TB or do worse.
Lastly, when you get on the 403 at Trinity Rd the next exit is Garden Ave in Brantford. If police, or anyone else, had decided to pursue them they would have been trapped on the 403 for 15 kilometres before an exit presented itself. The Wilson route provides quick access to a literal maze of sideroads in the rural areas as an escape route.
There is also this piece: someone further back in the threads said TB mentioned he was taking the buyers for a test drive at the fairgrounds. The fairgrounds sit at the corner of Trinity and Wilson. So turning left onto Wilson in expectation of making a U-turn back to Trinity or another sideroad back to TB's home on Trinity may have been TB's desired route for the test drive. But once on Wilson the perps just kept going all the way into Brantford. Food for thought.