Why should they offer you the lower price in the first place?
Capitalism works on the premise that market prices are based on what people will pay, and most people pay the asking price.
In your case you quibbled this and were passed to the Customer Retention Department who are authorised to offer various discounts based. I did the same for my car insurance and got a £50 Tesco gift card.
If everyone did the same as you the company would either make no money, or would have to raise prices, because believe it or not, most companies are not out to ripped off their customers, the pricing structure would be cost +% margin, this margin will be calculated on the cost of selling the item, plus cost of running the company, plus a certain level of profit. In your case the profit will have been removed.