Older movies will look horrible on DVD on modern TVs unless they are remastered. My guess is that the studios don't think they can sell enough copies to justify the expense.
I am surprised considering some of the utter crap that ends up on even Blue Ray.
That is entirely possible but there should be a way to do so. Tobacco Road is one of my favorites that didn't make this list. Mr. Frost is a modern film that is not available.
Old films can certainly look great on dvd, if they still have high-quality 35mm elements. There are some old films going back to the early-1930s that look absolutely stunning, if top-notch source material survived and was used.
Do you know what looks bad, though, on modern TVs? Television shows from the 1970s/80s that were shot on video-tape, like sitcoms and variety shows. Also, in the 1980s and maybe even early-1990s, a lot of otherwise nicely 35mm filmed tv-shows unfortunately used videotape for editing their master copies. Thus the masters are rather soft for high-definition sets, and look less impressive than a lot of older filmed tv-series from the 1950s/60s/70s.
Just ordered a DVD of the movie "The Wrong Box" with Michael Caine and Peter Sellers and a stellar cast of wacky British actors. I am really hoping it is a good edition as opposed to the VHS tape I got several years ago.