Typically in Indian private schools the students are responsible for purchasing textbooks at the start of the school year, not the schools (I don't know how it

Typically in Indian private schools the students are responsible for purchasing textbooks at the start of the school year, not the schools (I don't know how it works at public schools). And they won't change their textbook mid-year. Textbooks don't usually have much resale value, though I'm sure poor students buy them secondhand. They are paper-bound (and not even as sturdy as the average paperback) and tend to fall apart after a year unless you rebind them with cardboard. The quality of the paper isn't great. These are all good things because the books are inexpensive to purchase new (and it's possible some government subsidies may be involved). My guess is that the publishing company would prefer to keep printing the same book and make minor updates year-to-year, instead of investing in writing a whole new book. Unless the number of students enrolling increases dramatically they're not going to make more money by writing a new Python book.