Degenerate states form a whole subspace. The linear superposition of two degenerate states is again a state with the same eigenvalue. So your question is equivalent to:
can someone explain me why all vectors aren't orthogonal ?
However, it is always possible to choose an orthogonal basis in this subspace, and those eigenvectors ARE orthogonal.
We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling We Value Civility
• Positive and compassionate attitudes
• Patience while debating We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving