He got paid more to write more (not by the word but by the number of instalments in his stories, which were released in chapters serially) and tastes were different in the Victorian era. Authors could make shit up as they went along. Novels weren't edited in the same way and people expected a book to take a good long amount of time to read. People still enjoy his colourful characterisation but don't feel like you have to read him. Victorian literature, by our standards, is sentimental and slow.

Edit: I say this with love, I find the 19th century really interesting.