Sure, but they were for feature films, designed to be seen on large screens.
It's not like all TVs back then were the dinky little black-and-white things I grew up with. There were larger, more expensive color sets that could get a clear picture as long as the broadcast signal was strong enough.
Not to mention that it wasn't unusual for American TV episodes to get recut into movies for overseas theatrical release. The possibility of doing that for ST may have been incentive to make the FX good enough for the big screen. I think Roddenberry flirted with the idea of expanding the ST pilot to feature length if he didn't sell the series.
The eleven footer is larger than the movie Enterprise model or anything built for TNG.
You wouldn't expect a 1960s portable cassette player to be as compact as a 1980s Sony Walkman. Those models were made using more advanced techniques, constructed from fiberglas and plastic and the like, allowing greater detail at smaller size. The TOS ship was mostly wood. Make a wooden model too small, and you can't achieve the same level of detail, because wood has grain. Also, lighting and electrical components were larger in the '60s, so you needed a bigger model to fit them in. There were probably also advances in cameras, lenses, and lighting techniques that better conveyed the illusion of size in a smaller miniature.
Contemporary science fiction television series (Lost in Space, Gerry Anderson, Doctor Who) had models a couple of feet across, which was sufficient for the average black and white television screens of the time.
The
Jupiter 2 was 4 feet across, and it represented a much smaller, less detailed ship. The largest Eagle miniatures on
Space: 1999 were 44 inches; again, though, they represented much smaller ships than the
Enterprise. Moonbase Alpha was a 12-foot-wide model.
And indeed the original three foot Enterprise model was used on screen a number of times.
For distance shots, yes. For close-ups or shots of the ship flying in close to the camera, you needed the 12-footer. Indeed, those shots where the
Enterprise starts out as a dot in the distance and grows until it fills the screen, and then flies off into the distance again, were achieved by aligning and dissolving between shots of three different miniatures of different scales.