system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that some old TV shows on Netflix, like "The West Wing," look like they're in HD, while other old shows, like the British "House of Cards," look like they were filmed on video?
gpt
Some shows would have been recorded on tape (in which case you are pretty much limited to what they recorded) or shot on film - 16 mm (which is going to be sub-HD) or 35 mm (which is going to be better than HD). They may or may not have been captured with a 4x3 (SD) or 16x9 aspect ratio. This matters because you frame the shot differently: a 4x3 shoot may show stuff on the sides of the frame you don't want is you are looking at 16x9.

Now, you have this content on film. It has to be scanned, frame by frame, and possibly edited and or processed with FX to remove artifacts and whatever other problems came out during the process. Then there are things like the sets would have been poor quality because nobody could tell the difference in SD.

So, long story short, you may or may not have high quality content which may or may not be convertible to HD based on how it was recorded. Assuming you can get the original film and it is good quality, converting from film to HD can be expensive and time consuming and you may not want to pay for it depending on demand.

The good news is substantially everything is captured in digital HD or UHD now.