Why is watchmen on main label everything else that seen written by Alan Moore the Vertigo DC so why special?

Watchmen is not on the main DC Comics label, but is actually published under the Vertigo imprint, much like most other works by Alan Moore. Watchmen was published under the main DC Comics label for a short time in the early 1990s, but was later moved to Vertigo due to its mature content and complex themes that appealed to a more adult audience.

Other works written by Alan Moore that fall under the Vertigo DC label include:

- V for Vendetta

- The Ballad of Halo Jones

- From Hell

- Swamp Thing

- Miracleman

These works were created with the intention of exploring darker, more challenging, and often counter-cultural themes and narratives that might not have fit well within the traditional DC Comics continuity. The Vertigo label allowed Moore and other creators to push the boundaries of storytelling and experimentation within the DC universe, while still maintaining a connection to the larger DC Comics brand.