Why was there no 'Indian schedule' in the 1920 census?


I understand that there was a special 'Indian schedule' used to enumerate Native Americans for the 1900 and 1910 census, but that this schedule was discontinued from the 1920 census onwards. Among other things, this led to a undercount of the Native American population in 1920.

I was wondering if there was any known reason for this change (e.g., in order to reduce costs, or because of a change in priorities at the Census Bureau). I was not able to find any reference to the change in the Act of 1919 (https://www2.census.gov/programs-surveys/decennial/1920/1919-census-act.pdf), nor in various overviews of the 1920 census (e.g., https://www.census.gov/history/www/through_the_decades/index_of_questions/1920_1.html).

Thank you for your time.