You're thinking of film cameras used for motion pictures. While some shows were shot on 35mm or 16mm film, you're forgetting that a ton of television particularly in the 70s, 80s, and 90s was shot with 525-line analog NTSC TV cameras. This was especially true for lower budget productions like most PBS content. Nobody's bringing out the 35mm camera for an all-night live fundraising telethon, that's way too expensive.

This stuff was stored using reel to reel video tape recorders on 2" Quadruplex film or later on U-matic or Betacam tapes (if your station was lucky enough to get one. You might have just made do with 2" Quad til the station manager eventually bought a consumer VHS recorder some time in the 80s.)

Not all TV was shot on film, especially live TV which in the early days was often not even stored at all and a lot of what was shot on film was on 16mm which can be digitized at lower definition with out loss. But most important is that the lack of concern for preservation is not new. Most of the legacy media companies already lost considerable parts of their history well before digitization was even on the cards and were typically lazy about digitizing anything that wasn't immediately monetizeable once it was.

Could be low quality original archives that were then digitized at like 480p, depending on when they made the archive.