Why is each state entitled to a star on the national flag?

It was the 13 colonies who sacrificed in the battle against the British; then, after the fact, here come these Johnny Come Lately states saying, "Hey, can we join now that all the fighting is done?" And we say, "Sure! And by the way, here's a star for you."

I say, yeah, they can join, but only the elite 13 get a star -- you want a star, start your own country...