If INFPs balk at the idea of MBTI, then why they are over-represented in MBTI communities, often one of the most populous types & likely to be among the most active members?
If they resisted identifying with a type, then this would not be so.
Plus, several of the most well known MBTI authors are INFPs, including Isabel Myers herself. INFPs, along with the other INxx types, seem most likely to explore the theory deeply.
I see INFPs as being very interested in typology & eager to type themselves because we're generally big on
1) self-growth & self-understanding
2) searching for identity to ease our sense of alienation (many INFPs express great relief upon discovering their type, not a feeling of being pigeon-holed)
3) theories, especially ones that are connected to people, such as psychological theories