For it to make sense, language replacement (which is an observable phenomenon) would have to happen by communities learning a bunch of different languages and p

For it to make sense, language replacement (which is an observable phenomenon) would have to happen by communities learning a bunch of different languages and picking the one that they liked best. That's just not how it goes. You learn a new language to speak with new people that you're interested in, regardless of how weird and hard to learn their language is.