It could be a variety of things.

This is highly speculative, but the fact it’s been on the market for a year, and he is being difficicult, indicates a lot of things. Perhaps a part of him doesn’t really want to sell it? Perhaps he is attempting some poorly thought out negotiation tactic? Perhaps he is stringing you along, secretly hoping someone else comes and makes him a better offer?

In either case, make it very clear you are getting frustrated with the pace of negotiations, and hint that you still have other houses you’re looking at.

The house has been on the market for a year. He doesn’t have a lot of bargaining room.

Just put some pressure on him.