Why do Spaniards love to eat sunflower seeds?

Spaniards love to pass the time cracking salted sunflower shells open with their teeth one by one before eating the seeds inside, leaving behind a wet grey mess on the ground at football stadiums or on the street. What’s all this about Spain?

Why do Spaniards love to eat sunflower seeds?
Spaniards love to pass the time cracking salted sunflower shells open with their teeth one by one before eating the seeds inside, leaving behind a wet grey mess on the ground at football stadiums or on the street. What’s all this about Spain?