Why is Africa Antarctica Asia Australia Europe North America South called continents?

The seven regions you mentioned (Africa, Antarctica, Asia, Australia, Europe, North America, and South America) are indeed not all continents. Here's the proper classification:

Continents:

1. Africa

2. Antarctica

3. Asia

4. Australia

5. Europe

6. North America

7. South America

These seven regions are considered CONTINENTS.

Oceans:

1. Arctic Ocean

2. Atlantic Ocean

3. Indian Ocean

4. Pacific Ocean

* Southern Ocean [not universally recognized]*

The areas you listed as "called continents" are all, in fact, considered continents. The term "continent" refers to large landmasses separated by oceans. Each of the regions you mentioned meets this criterion and is therefore considered a continent.