Instructions say to mark BLANK if record lists "Native of-----." That is not the same as "Nativity." Why is everyone listing the birth location if the record says "Native of -----?"
It could be because they aren't reading the PI or they just don't care. All we can do as reviewers is to mark that field blank.
Perhaps "native of" has different meanings in different countries. In records I research relating to Durham, England, the term "native of" is always synonymous with "place of birth".
Either this is not the case in Missouri records, or the person who wrote the PI isn't understanding the meaning of the term in the sense it is probably being used here. If someone is just being pedantic here it is a great shame, as the place of birth could end up being missing from these indexed records when including it would be of great use to researchers (especially if there are no linked images).