Here's why:
* Common nouns refer to general categories of people, places, or things.
* Proper nouns are specific names for individual people, places, or things and are always capitalized.
"International Teams" is a general term that could refer to any group of people from different countries working together. It's not a specific name, so it's a common noun.
If you were referring to a specific team with a name, like "The International Team" or "The Global Squad", then it would be a proper noun and capitalized.