What are disadvantages of putting utility classes only into a namespace in PHP?

In a project I defined several utility classes (currently in the global namespace).

Now I thought of moving them as static methods into a utility class. In order to avoid naming conflicts, I could also simply use a namespace.

What are possible reasons to anyway move them into a utility class?

The only thing that came to my mind is, that I can't take advanatage of the classloader, if the methods are not within a class.