A lot of "catalog" movies being shown in HD on cable/satellite (or even being authored onto Blu-ray) are using old HD telecine based sources originally prepared for DVD.
Unless the film print is perfectly clean and the HD telecine equipment is operating perfectly, you're going to see problems with such video transfers. The low resolution of DVD Video hid many of the flaws of those sources, but the flaws show up all too well when seen in high definition and on higher bit rate formats like Blu-ray. Dirt specs, tiny scratches, image movement (such as side-weave), weaker color quality and an overall softer look are all things that can be seen in a cheaper, less accurate HD telecine video transfer.
It costs more money to scan the original camera negatives (or best surviving elements) and process them via digital intermediate. But the results are so much more accurate. That method is a lot better than just grabbing some old 2nd or 3rd generation print and running it through a telecine.
That's the way they looked in the movie theatres back then, but we didn't know any better.
Before blockbusters like
Jaws and
Star Wars were released, most movies had a pretty limited number of prints in their inventory. It wasn't until the 1980s that studios opened big movies with more than a couple thousand 35mm prints. The movies that had fewer prints saw those prints travel to numerous theaters and get played so much that the print would finally end up badly faded and damaged. Today, it's common to see a first run multiplex get 2 or 3 prints of a certain movie on opening day and lose 2 of those prints after a couple of weeks. Those extra prints often get shredded and recycled rather than go to any other theaters.
I remember seeing a lot of movies at drive-in theaters when I was just a kid. Drive-in theaters usually received different prints deliberately made brighter (and arguably more faded looking) to counter the problem of throwing a 35mm image onto huge, outdoor screens.