I'm not saying that they are not actually good, especially from a technical angle. However, how many people have read original Dicken's work, and not seen the adaptations? A Christmas Carol might be one of the most adapted stories of all time. And it is one of the few Dicken's works that most people can name... because they've seen the movie adaptations.
And the only other one I can think that most people know is Oliver Twist... which is again because of the movie adaptation, and frankly, despite owning the book for several years, I don't even remember what happens in it.
And neither does culture. Take for example, the ultimate expression of what I'm talking about.
Frankenstein and Dracula. I've read the original Frankenstein, and it is a very good work with very powerful theme... and the vast majority of people don't even realize the "monster's" name isn't Frankenstein, but Adam. What has survived and endured is only "Frankenstein by Mary Shelley" in the most shallow of senses.
Most Dracula adaptations look, act and contain next to nothing of the original work from Bram Stoker, and Bram's work was a rip-off to begin with.
Just as we know that just because something is popular doesn't make it good, just because something is old and well-known doesn't mean that the adaptation cannot be better or more appealing. What often holds adaptations back, in my opinion, is RELYING on the good-will and popularity of the original, of thinking "the story has been around for a hundred years, so surely the strength of the story alone will uphold it and make it good"
But, that isn't the case. Many of these stories hit on very common themes and tropes, and are only buoyed by technical craft. Many of the classics that the people who wrote these tales would have pointed to and said "this work shall live on forever" have been largely forgotten, buried under the work they inspired which achieved something greater than the original. Adaptations can be better and more impactful than the original, they can take the original to places it never could reach on its own. They can also crash and burn. The key is not "is it an adaptation" the key is "is it well-made and technically masterful"