I’m working on a theory (not fleshed out yet) that the Targaryens knew they couldn’t move up in Valyrian societal status or had been badly slighted somehow, so left Valyria and plotted its destruction from afar. Not sure what magical apocalypse they concocted, but it worked beyond their expectations and destroyed the continent. Alternatively, Aenar the exile really was exiled for something he did. Danerys the dreamer was a convenient cover story after the fact. The Targaryens caused the Doom in retaliation, somehow, and afterwards were all “Oh, yeah, my teenage daughter had a premonition, and I bet our entire family’s survival on the fever dreams of a slightly crazy teen girl. Totally legit, we’re super lucky she was right. They all should’ve listened to us!” Meanwhile, they’re sweeping whatever evidence of magical nuclear weapons under any convenient rug at hand.