OK, "Green Acres", isn't actually "Game of Thrones", with respect to its potential for sales of units. I would imagine that makes the producers largely unwilling to spend the big bucks on remastering it. Its target, after all, amounts to a "niche audience".
As for the quality on the TV "side band" digital channels, first they're 480i, not the 720p or 1060i of the primary channel. Second, I'm pretty sure you'll find the bit rate to be much less than a DVD playing the same content. The result is with anything less than a "5 x 5" signal, you'll get "compression artifacts". Those little squares in the picture which outline the Mpeg compression area.
Despite your contempt for DVD's low resolution, its high bit rate allows it to be scaled up quite respectably. No, it's not 4K Blu-ray, but given good production, it's quite adequate for a pleasant viewing experience.
As for your, "must have been shot on film" observation, keep in mind most movie film is ISO 100, and pretty darned grainy as well. The lack of apparent grain is "visual retention", which is the inability of human mind to "refresh the scene", before the next frame is displayed. So, the grain is basically jumping to different points in the image, and your eyes can't keep up with it. So, for all intents and purposes, the lack of grain in movie film, is naught but an, "optical illusion".
BTW, the standard cinema frame rate is only 24 fps.