The relevant bit being "Verifiers SHOULD permit claimants to use 'paste' functionality when entering a memorized secret. This facilitates the use of password managers, which are widely used and in many cases increase the likelihood that users will choose stronger memorized secrets."

But that's a recent change to the NIST guidance. Searching for "Bill Burr NIST" will turn up recent stories about the original author's regret of a lot of the password recommendations from the original publication in 2003 that survived until the update this year.