Most good distributors are going to have existing clients, commitments and contracts. Sometimes the price to you or I will be based on making it worthwhile to deplete their stock-pile and potentially have to source replacements in a pinch later, because those contracts will include things like “will supply x board-feet in x shape in x timeframe at x price”, with penalties for non-compliance.

If you have the time to shop-around, by all means do so, but otherwise … yours is the pinch they were trying to avoid for themselves by quoting that price. It could also just be that they don’t stock below a certain quality/price-point, that you or I would find acceptable, but not their regular clients.

Did you check their pricing for other cuts?