https://constitution.congress.gov/browse/article-1/section-2...

> The actual Enumeration shall be made within three Years after the first Meeting of the Congress of the United States, and within every subsequent Term of ten Years, in such Manner as they shall by Law direct.

The key thing you're missing is "in such Manner as they shall by Law direct".

Congress has passed a whole bunch of laws that attach additional responsibilities to the census for the purpose of supporting government decisions.

The Permanent Census Office Act of 1902 for example, which established the census office and tacked on "an annual survey of cotton production, and other economic censuses" https://www.census.gov/about/history/historical-censuses-and...