Why did Michel Foucault move from archaeology to genealogy after 1971?

Michel Foucault shifted from archaeology to genealogy after 1971 primarily because he found his earlier "archaeology of knowledge" method to be limited in its ability to analyze the dynamics of power.1

While archaeology allowed Foucault to examine the local qualities of past conceptions of humanity and the structure of discourses (or épistémès), its consideration of the relationship between power and knowledge was, at best, partial or oblique. By adopting genealogy, Foucault was able to trace the historical contingencies, accidents, and illicit relations that formed the ancestry of accepted theories in the human sciences. This method allowed him to expose the artificiality of the dividing lines between the "normal" and the "deviant," as seen in his works on the criminal character and the history of sexuality.1

Ultimately, genealogy provided a more robust framework for investigating the complex dynamics of power-knowledge, enabling Foucault to better understand how individuals are shaped into subjects through historically specific practices of domination and discipline.1