Dragonflight was a marketing move, wotlk has a lot of dragons especially early so it will generate interest in the dragon element, also I believe they will release cataclysm classic afterwards and Dragonflight aims to boost it by generating even more interest for dragons. It was a 100% marketing move and this proves that classic hurts their vision for retail, they now don't focus on strong lore elements but they aim to make them boost each other.