First of all, the Big Read list is nowhere near definitive.
I suspect that there are so many books on there that people have seen as movies for precisely that reason -- movies can give a distorted view of the book.
Who do you see as Mr Darcy?
Or to name a book not on the list --The Scarlet Pimpernel. Percy Blakeney is fair haired but Richard E Grant who played him in the most recent television adaptation is dark haired.
Or perhaps they are books that people talk about.
or books that people think they know.
I did not say that I loved all the books. Some of the books I had problems with. But that is down to my own tastes. And the books are often very different to the movies/television/popular culture verision. Gordon Brown as Heathcliff anyone?
Second, it depends who compiles the book list. For example there is no Mark Twain, Nathaniel Hawthorne or even Ernest Hemingway. You have one Steinbeck.
There is no Willa Cather or William Faulkner. Where is Henry James? Graham Greene? Sir Walter Scott? I could go on and on but you get the picture. The intriguing thing for me was that I had read so many of the books. But I suspect that is more serendipity than anything.
Third, I like Dickens. A Tale of Two Cities is one of my favourites, but it does take awhile to get into. What it is interesting is that until about the 1930s, he was simply held to be a popular rather than a great writer. In other words, he was writing for the commercial market and it was a very particular commercial market. He does not suit everyone, but I do think he is a good story teller.
But the main message should be to read and to read widely.