Lithgow is, undeniably, a much bigger name than Rylance, at least in his native U.S.. (Although it’s kind of weird that they’re looking to cast an American actor in the role of one of the iconic British wizards;

Hollywood has a not-so-mysterious way of casting who they want for roles in films and television shows with major IPs. There is usually a breadcrumb trail that you can trace back to a few previous projects that will help you understand why a choice was made for a particular actor.

US actor John Lithgow is reportedly set to take on the role of Dumbledore as the makers of the new Harry Potter TV series start to assemble their cast. The veteran Oscar-nominated star is "in final talks" to sign up to play the Hogwarts headmaster, according to film and TV industry outlets Variety and Deadline.