Why do schools keep buying new textbooks, when they could very well make one edition and use that forever?

What I mean is, Algebra and Biology are not cl subjects that are going to change. Why can't' they just make one set of textbooks, and then use that for the next 30-40 years? Why do textbook companies keep printing out new textbooks and selling them for a hundred of dollars for EACH individual textbook, and make schools buy them every 4-5 years? We should just buy ONE textbook edition for subjects like Math and Science and Art, and Language and even History. Use that one textbook for the next 50 years and make a huge first run print and use those sets of books for years even decades , or better yet, make the textbooks of such a quality that the pages are as thick so that they can have a life expectancy of 10 years or so.