I'm not sure this is a fair representation. Rails didn't "guess wrong" too many times. They chose the best option available at the time. Remember, CoffeeScript was used in Rails in 2010! Brendan Eich even borrowed many ideas from CoffeeScript in subsequent versions of JavaScript. Ditto, the asset pipeline solved a great number of problems for many years. With recent advances in web browsers, many of these problems aren't really problems, so it's less relevant, and Rails has to take advantage of import maps as an alternative.