That’s because the original screenplay was written by Rod Serling (as mentioned just above here), who wrote in that style — I don’t think it’s a defect, myself.
Even when I first saw it, I was annoyed at it as science fiction. Gorgeous costumes and sets, but it didn’t make a damned bit of sense. The talking English, as mentioned, is wrong on so many levels. The survival of the Statue of Liberty.
The very idea that the ship could end up on Earth at all defies belief – it’s as if you set out in a powered boat from, say, Manhattan with a working navigational system bound for Australia, and you get off the boat and find yourself in New York. Worse, actualy, since the odds of your coming to a star with habitable planets simply by chance in space is negligible. You can fanwank about “systems set to automatically return you home” all you want, but it’s all bull. You wouldn’t buy a blunder like this in, say, a World war II movie.
But even if we ignore that, the Ape Civilization makes not a lick of sense. Serling reportedly wanted to show something very much like the modern world, instead of the Organic Shapes in the Wilderness the movie had. (although I’ll grant that it had a wonderful sense of Weird to it). But a society of so few people, at such an industrial level (and stated several times to be on the edge of starvation because of the actions of the humans) just wouldn’t have the time or resources for Museums and Professional Scientists and Zoos – they’d be too damned busy trying to stay alive, and you’d expect them to be at a level like, say, Colonial America. Or maybe, for a cultural change, Japan under the Shoguns. I sure don’t expect dedicated Museums with glass-encased dioramas, and people who could afford to spend most of their time theorizing. If you’re starving, even the scientists end up working the plows.
I found the next movie embarassaing. If you think the original flick was too 60s-bound, watch the second one with its placard-carrying protestors facing off against the militaristic gorillas. And the series went downhill after that.
Pierre Boulle’s novel is worth the read. It’s very different, and Taylor and company aren’t on Earth through the bulk of the film (and Apes have space travel). It’s been argued that the title should be less pompously be translated as “Monkey Planet”, and it’s more obviously tongue-in-cheek. An interesting contrast is L. Sprague de Camp and P. Schuyler Miller’s Genus Homo, which features a bunch of 20th century folks dumped in a future Earth run by primates, who originally get stuck in the zoo because the apes don’t realize they’re intelligent. Just as in the movie (but NOT in Boulle’s book), the apes are segregated by variety into social classes, wiyth chimps as the brains and gorillas as the enforcers. I suspect that Serling o whoever is responsible for that feature of the movie developed it independently, though.