For practicability and usability
Like I said earlier on, design is around and surrounds us in our daily lives, our tables, chairs, beds, cups, plates, toothbrushes, shoes, clothes, etc. Every single object around is somehow designed to give us a beautiful experience in using them.
Some of our objects are designed to create visual harmony and contribute to our quietude, and some are designed to make their use comfortable to us or to gain space. Objects are designed to help us use them easily, or even, hard sometimes, and make them practical.