When a MatrixProject is loaded, the axes are re-ordered with Collections.sort - see https://github.com/jenkinsci/jenkins/blob/80a3f1fe0c87e18c113c05a1a9ac55a04f5d1b49/core/src/main/java/hudson/matrix/MatrixProject.java#L469

But it's distinctly possible that one would want to have the axes ordered in a specific way, regardless of alphanumeric sorting. I'm honestly not sure if there's ever a case where we would actually want to force a re-ordering. I'd think that line should be removed.