The main process by which languages become simpler (when they do. It is not a universal rule) is when large numbers of adults have to learn the language. This u

The main process by which languages become simpler (when they do. It is not a universal rule) is when large numbers of adults have to learn the language. This usually happens during mass migrations involving intermarriage. The newcomers don’t learn all the complex rules and nuances. They tend to leave out some of the more complex parts. If there are enough of these newcomers, then their children start speaking a version of the language that has been simplified by their parent. English went through this when the Norse invaded England and controlled up to 3/4 of it for several hundred years. As they did not have a large social separation from the English, they tended to intermarry with the English, and because their own language was similar but not the same, it was easier to speak a simpler kind of “pidgin” based on Anglo-Saxon but dropping things like gender and declensions that didn’t match the Norse versions. When the Normans invaded, they stayed socially separated from the English for much longer and didn’t try to learn English, so there was no repeat of the simplification process. In contrast, the Norman French vocabulary migrated into English and seriously complicated the spellings in English.