Because of the raw materials you could obtain from a dragon’s body, even the smaller version called wyvren in itself achieved a decent price in trades.
To say nothing about a large grown drake like the one Burkhart-san had defeated before, where there was no unusable body part to the degree that all of it could be called valuable.
Blood, meat, scales, bones and a magic core to the extent that it couldn’t be compared to any other monster.
Raw materials with the dragon attribute itself appeared on the market once in 50 years and even that could be called fast. I heard that the trade prices for the materials were terrifying.