His reason is almost certainly money. An agent's commission isn't insignificant. It's the opportunity cost of, well... what he's doing.
If he's talking with contractors, he's probably also trying to figure out how to fix it up or modify it. I didn't need to talk with any contractors at all, so I don't know whether or not an agent would have helped.
If the seller is paying for "your" agent, is she really yours in the incentivized sense?
eg. Zuckerberg's college buddy who fronted the money for early FB servers was sure that "his" attorneys had his back, right up until they stabbed him, because they were paid by Zuckerberg.
