Maybe it’s just a selective effect: some actors like, or don’t mind, science fiction roles, and once they’ve been in a well-known SF role directors and casting agents think of them when another role opens. But it seems like some actors who had previously been known for other genres get trapped in a SF “ghetto”. Is this real? The following come to mind:
I don’t think Charlton Heston or Ernest Borgnine, despite many appearances in SF, were ever typecast as “SF actors”.
Neither was James Caan, despite lots of SF films (Countdown, Alien Nation, Rollerball, The Lathe of Heaven)
I think the first role people think of when they think of Heston is Ben Hur. Yeah, folks’ll also remember Planet of the Apes and Soylent Green, but for those, I think they’re mostly just remembering his delivery of the climactic lines.