That's not how the Berne Convention works. Copyright is applied automatically. You can't just assume people who publish works without a license "don't care". Maybe they don't want to give you a license and want to retain all of their rights under copyright law.

I always put licenses on all of my works (including presentations, blog posts, images, as well as code obviously). All of them are licenses which make it clear that I wish to provide people more freedom than granted by default under copyright law (in counties that follow the Berne Convention).