It seems sort of questionable to use the list of things to not scrape as a starting point for scraping.... I mean, I get it's not actually enforced.
The robots.txt does not exclusively list what not to scrape.
It provides information on which parts are allowed and wich are not (disallowed).
It also provides sitemaps for crawlers as a starting point with more information (eg. which sites are available and how often are they updated, etc.)