How did Good Omens manage to put together a star-studded cast?

Indiewire

Benedict Cumberbatch, playing Satan, was announced Wednesday as the latest big name to join the Amazon limited series based on Neil Gaiman's novel. The Good Omens cast also includes Frances McDormand, Michael Sheen, David Tennant, Nick Offerman, Jon Hamm, Miranda Richardson, Michael McKean and Jack Whithall. Gaiman noted at the TV press tour that Hamm was a big fan of the book, while Offerman offered to buy his own ticket to South Africa to be part of the limited series.