If autism is classified as a "neurodevelopmental condition," then why isn't a "normally developing" brain similarly labelled as a "condition?"

Once again, this is related to the "othering" that happens as part of the process whereby power structures in society are maintained. One of the promises made within theses structures is that we will be kept safe from threats - internal and external. An autist looks like lots of people but can't be relied upon to behave like them and is therefore a threat. This is okay, as long as the threat is seen to be kept at arms length, or have their behaviour moulded to fit in with what appears to be "safe".