ID vs Class

Question

In CSS the major difference is that IDs can only be applied once per page, while classes can be used as many times on a page as needed. My question is why? Is that because ID works as a global attribute and class not or smth else in the logic?
https://code.sololearn.com/W5HDCnlq0XZ8/?ref=app

Answer 1

Class is used to target various element at a time hence it is common for all if they have similar style to do.
Id is used to target a single element hence it should be different for all.

And class is also a global attribute in html 5.

Answer 2

Divya Mohan tnx