Sprachbunds

[Forbes]

There is no doubt that Sprachbunds exist. How though do they come about when the members are not closely related? What makes the speakers of one language adopt a feature of another? It is difficult to imagine people thinking: "Postpositive articles! We'll have some of that!"

[Daniel]

Close contact. Sprachbunds aren't a sharply defined phenomenon, but just the extreme end of prolonged close contact between languages. Bilingualism results in convergence, along with borrowing and other factors.

It is difficult to imagine people thinking: "Postpositive articles! We'll have some of that!"

But that's not the case for internal change either. Language change is just the result of language use. When a language is used a certain way, that shapes its future. When languages are used together, that shapes their futures.

[Forbes]

Languages meet and mix in all sorts of ways for various reasons. I can see that when people need to communicate they will make concessions, but the grammar of one language "interfering" with another seems extreme. Adoption by a group of languages of grammatical features does not in fact increase mutual intelligibility between them, so it is puzzling why it happens.