As per this question and the answers provided therein, Dragons are of the "always X" alignment. Which means…
Always: The creature is born with the indicated alignment. The creature may have a
hereditary predisposition to the alignment or come from a plane that predetermines it. It
is possible for individuals to change alignment, but such individuals are either unique
or rare exceptions.
A description that is usually reserved for such races as Demons, or positive/negative energy aligned creatures… and yet, is also applied to dragons.
This strikes me as somewhat odd, given that dragons are intelligent creatures capable of making decisions of their own, not directly tied to any particular good/bad plane of energy.
What then is the in-canon reason for Dragons being "Always X" alignment?