Conservative, in this case, means what it means in every case where it has a meaning: preferring not to change without a good reason. A practice having survive

Conservative, in this case, means what it means in every case where it has a meaning: preferring not to change without a good reason. A practice having survived for centuries is not necessarily a good thing, but it at least indicates that many generations of people found it valuable, and suggests to the conservative that it might be better preserved than abandoned. I think an understanding of this difference in our outlook would probably answer the rest of your questions.