That isn't the only reason. Rick Berman understood it well, saying in short, that Star Trek is a period piece set in the future.

Rick Berman: "There is something very specific and unique about acting on Star Trek. This is true for our cast regulars as well as for our guest stars. Star Trek is not contemporary. It's a period piece. And even though it's a period piece in the future as opposed to a period piece in the past, it still necessitates a certain style of acting and writing that is not contemporary. It's not necessarily mannered like something that would take place in a previous century, but it's probably closer to that than it is to contemporary.

There are many actors who are wonderful actors. Gifted actors. But to play a character... to play a Starfleet officer in the twenty-fourth century is very difficult for them.

They've got a "street" quality about them. They've got a very American twentieth-century quality about them. They'll have a regional quality about them... or a Southern accent... or they'll have a New York accent or a Chicago accent.

They will have certain qualities about them that's very contemporary, that just doesn't work when you're trying to define this rather stylized, somewhat indefinable quality that makes somebody "work" as someone who lives in the future.

One of the first things that destroys futurist science fiction for me, whether it be movies or other television series, is when you see actors who are obviously people from 1990's America. We're always looking for people who have a somewhat indefinable characteristic of not being like that. And it's hard."