The Name Was The Same

There was something that puzzled me, and I mean greatly puzzled me, when I was little. In order to understand my confusion, you need to know that my maternal grandfather's first name was Nathan.
Every now and then, my family would go to

for a meal. Baba preferred to sit down to eat, so we'd go inside and enjoy table service.
My usual meal was a hot dog or a hamburger (I was crazy about their hamburgers!) a chocolate shake or a cup of hot chocolate, sometimes corn on the cob. There was one item I invariably
ordered: French fries.
So where does the confusion come in?
Remember, my grandfather's first name was Nathan.
The place was called Nathan's.
We've established these two facts.
I could never understand why we had to pay for our meals, since it was quite
obvious to me that my Grandpa owned the place!