Here's why:
* Abstract nouns represent ideas, concepts, qualities, or states of being. They are not physical things you can touch.
* Concrete nouns represent physical things you can touch or see.
Tradition is an idea or concept about customs, beliefs, or practices passed down through generations. You can't physically hold or touch "tradition" itself.
You might see evidence of tradition in physical objects, like a family heirloom, or in actions, like a specific holiday celebration, but the concept of tradition itself is abstract.