If you look at any old movie, when they show the title, they always include the copyright info in the same frame of film. As an example, North by Northwest was just on TV. In tiny print at the bottom of the frame that had the title, it said: “Film by Loews Incorporated. All rights on this motion picture reserved under international conventions.” Standard legalese, and quite similar to what is printed at the bottom of this very page.
I assume this was considered a legal requirement at the time. But they don’t do this anymore. So why’d they stop?
This is a WAG here, but it might be because they started placing the credits at the end of films instead of at the beginning. When everything else got moved to the end, I suspect that’s when the copyright info got moved there as well.
They probably thought the most pertinent information was the title, the stars, and the main crew. Thus, those stayed at the beginning (the credits being moved was discussed on the board a while back, but I don’t have time to look it up just now) whereas what was seen as less pertinent information (the rest of the crew, the rest of the credits, the thanks, and the credits) got moved to the end. Since the entire film as seen as one entity, the copyright can come at the end representing the whole.
Again, though, these are just WAG’s.
In 1977, the copyright law was amended so that placement of copyright could be in any location “as to give reasonable notice of the claim of copyright.” Previous to that, there was a specific location. Once that was changed, Hollywood decided that it didn’t need to be at the beginning.