Uncredited actors, and the credits themselves

I don't know for sure. It may be that named performers had to be paid more. (I don't know that this was the case, but money is ultimatrely at the back of everything, isn't it?) But this Hollywood practice was not followed in Britain during the same period, where for the most part all the actors (or at least nearly all) were listed in the after-film credits.

Another oddity is that often the studios would list someone -- usually a starlet whose career they were trying to boost -- in a film in which she had almost no lines or screen time, just to get her exposure, while ignoring other actors whose roles were significant and important. For example, the US/UK co-production No Highway in the Sky (1951) listed two women in its cast who had few scenes, virtually no dialogue and played basically unimportant minor characters, while not crediting over half a dozen well-known major actors with large and crucial roles.

However, a funny (and absurd) instance of this is in the closing credits of It Came From Outer Space in 1953, one of the very few films of the time that listed all the credits at the end of the film instead of at the beginning. While as usual ignoring some established actors in supporting parts, the closing credits there not only named the main actors but showed them, using scenes from the film. But the last person shown was a Universal starlet named Kathleen Hughes, who had a very brief, single scene at the sheriff's office with just a couple of lines, playing Russell Johnson's girlfriend. First of all, her role was smaller than almost every other actor in the film, yet she was credited while others weren't. But second, instead of showing her in her one scene in the movie, they showed her in extraneous footage wearing a low-cut evening dress, thrusting her breasts toward the camera, while the music swelled to make her seem some sort of major star. The effect was both hilarious and utterly idiotic. At least The Thing didn't do that with Mrs. Chapman!

Phil Carey was a good, reliable actor. I don't think he was in The Thing but I'd have to look at that opening scene again. I never particularly noticed the actor you speak of. Carey began his film career in 1951 at Warner Bros. and TTFAW was an RKO picture, but it's possible he played a bit elsewhere before going under contract at Warner.