[sph]

https://example.com/.well-known/ is the conventional place these days to store this type of meta-information.

favicon.ico and robots.txt predate this convention, so they keep littering our server root directories.

[capableweb]

Just because they are available at example.com/robots.txt doesn't mean you need to have the actual files in /var/www/html/robots.txt, redirect rules are trivial to add in most (if not all) web server software.