I only guess but maybe because in Swift they encourage you to use value types whenever possible, so you have to make a conscious decision when you are steering

I only guess but maybe because in Swift they encourage you to use value types whenever possible, so you have to make a conscious decision when you are steering away from the default. This way it emphasises a particular way of reasoning about the code. Also, it's pretty straightforward to create a reference type of a value type if you end up need it: Just create a new type that is a reference type and has the value type as a property. No?