Though dragons were thought to be largely extinct, it's very hard to prove a negative. How would you go about proving there are no dragons? By not meeting any, obviously, but of course that gets blown out of the water the day you do actually run into one. After that, what do you do? Reclassify it as a species that isn't technically a dragon? Negotiate with it? Ask it stupid questions? As long as it isn't immediately eating everyone, why not try all of the above?