Radio was it.

[optimistic pessimist]

In a documentary film about a racehorse called "Seabiscuit", a former jockey trainer made the following remark.
"This is a time before sports on television. Radio was it. Horse racing on the radio was popular nationwide and it was a natural. Seabiscuit was a major star."

What does "it" refer to in this context?

Source: 03:11 of Seabiscuit: America's Legendary Racehorse (

)

 

[Tarheel]

Radio was the thing. In other words, that was what people listened to for news and entertainment. It was before television, so radio was it.

 

[Barque]

Yes. The speaker may also have meant that radio was all there was to follow it live, from somewhere else.

 

[emsr2d2]

In this kind of context, "it" means "everything" or "everything that is/was available".

A: Can you lend me six dollars?
B: I'm sorry but I can't. I've got four dollars and that's it.

A: Did you have a games console when you were a kid?
B: No. We had a small black-and-white TV but that was it.

A: I'm really hungry. Shall I knock up a huge mushroom risotto?
B: You'll have trouble. There's a courgette and a couple of carrots in the fridge and that's it.