I sympathize with the resellers here. Often times the original owner cannot be contacted. Maybe they are dead and the machine came form an estate sale. Maybe it was sold on consignment or something. Maybe the original owner is just very difficult to find.
I bought a MacBook off an eBay seller, and had to deal with this shit. It took the seller forever but by some miracle he was able to track down and contact the original owner so he could unlock it. Without this hassle, a perfectly good computer would have been e-waste in a landfill somewhere.
Frustrating the legitimate second hand market and the ecological impact of all this waste is a high price to pay for mere anti-theft. Companies are very eager to kill the secondary market for their goods, and accepting this scheme plays into Apple’s hands.