grammar - Why Does the Format "_____ Is" When Asking a Question Sound Correct in Some Situations, but Not in Others

For context, I am an Assistant Language Teacher for ESL. Part of my job is offering a native speaker's perspective, the main teachers are not native speakers, and I was asked about this. To the other teachers, this structure is always acceptable, but I am not sure about this.

I realized that in some situations, "____ is" sounds like a perfectly fine answer, but in other cases it doesn't. I want to be able to explain to the other teachers and my students why that is, or what the rule is.

For example:

-Who is going to the game tonight?
-She is.

This sounds fine to me.

-What is the most popular sport in America?
-Football is.

This seems okay enough to me.

-What is the name of this book?
-Catcher in the Rye is.

This, to me, sounds off. I'm assuming that other native speakers feel the same way, but I can't seem to figure out the rule. Also, is this actually grammatically correct, but it just feels off?

I should add too that the previous native speakers in my position had told the main teachers that "____ is" is acceptable, and the main teachers are under the impression that they said it is okay in all contexts. So, if I'm going to say that it only works some of the time, I need to explain why.