If you were beautiful, many people would see only the beauty. They would pay no attention to how intelligent, or kind, or respectful, etc. You were. So, you would have to prove to someone that you actually knew what you were talking about.
On the other hand, if you were intelligent but not beautiful - such a subjective term - they would focus instead on your intelligence.
There are many people that would walk away from dating someone who is intelligent because they want eye candy on their arm.