Because the most inconsistent thing in that scene ends up being Obi Wan choosing from the entire prequel canon the idea that Anakin was "the best pilot in the galaxy".
Seriously, he tells him that:
his dad was a good pilot.
his dad was a cunning warrior and a good friend
his dad wanted him to have his lightsaber when he was old enough.
It's not just that the facts of the conversation are wrong, it's that the tone of the conversation is entirely off for what ended up being canon, even before the prequels, but DEFINITELY after the prequels.
People latch on to the "Vader" thing, and who's to say, but it's absolutely clear watching it that the backstory they hint either makes no sense, is different than what they ended up doing, or both.