Dragons are a bit mysterious and mythical. Maybe were more prevalent in the past, but those records are old and incomplete. They are sort of cryptids.
Drauven dragon: a natural sort of dragon. Drauven worship dragons, dragons will use drauven as pawns. Mabye drauven are trying to turn themselves into dragons?
Thrixl dragon: self-authored -- "let's be dragons" and then they were. Thrixl dragons are somewhat removed from the thrixl hierarchy.
Dragons evolve naturally in relation to magic being in a place. Magic focused their evolution. They are magical or can use magic or devour magic.
Dragons are very local: dependent on magical microclimate. Also maybe dependent on some geographical microclimates.
Not a lot of existing lore about heroes encountering/fighting dragons -- until the hero legacy.
Dragons are sentient -- they can talk. They have no inherent alignment or personality traits; dragons come in many flavors of personality. Dragons are very varied as individuals.
Dragons are as much characters as they are fights.
Why are dragons not prevalent anymore? Maybe not in human-controlled lands, but more likely to find them further away.
Dragons, in fights, are about the level of bosses.