Brave urges federal employees to use a browser that blocks advertising by default. Without this, federal employees would be vulnerable to malvertising, which could allow foreign and domestic threat actors to gain access to government devices or a foothold in sensitive networks. In June 2018, the National Security Agency issued public guidance related to the threat posed by malicious advertisements. Brave sent this letter on the same day they officially released Brave Browser 1.0, this can be seen as a clever marketing ploy by the browser developers.
Source: https://www.bleepingcomputer.com/news/software/brave-urges-congress-to-require-ad-blocking-browsers-for-govt-employees/