jepe wrote
One reason is, that this allows customers to pay less for a very good software.
Another reason is, that users are free to modify the translations. For example, if you find a typo from the translation you can easily fix it yourself.
Or, if you speak a minority language to which no official translations aren't available you can translate the product yourself and share your translation with your community. You can't do that with many products, but you can do it with our products.