Why did Charles Lyell repeatedly revise Principles of Geology?

Charles Lyell repeatedly revised his seminal work, Principles of Geology, primarily because the book was highly successful and sold well, necessitating frequent new editions.1

To keep these editions current and accurate, Lyell actively gathered new data during his extensive summer travels and geological excursions, such as his visits to Scandinavia in 1834 and 1837. Furthermore, because his method of scientific inquiry was novel and initially considered mildly heretical, Lyell used these revisions to refine his clear exposition of methodology, which was highly regarded by the scientific community. Over time, these revisions also allowed him to update his work as his own perspectives evolved, including his eventual departure from earlier antiprogressivist views regarding the development of life.12