Incremental static generation not working in version 13

Does ISR works for anyone in NextJS 13 Beta version?

I am doing the following by using revalidate.

export const revalidate = 15;

When I perform npm run build, it still ends up as a SSG (static site generated) page.

The symbol is empty white.

What am I missing? I was expecting the page to be ISR.

P.S: Also tried with fetch api and { next: { revalidate: 15 }} and outcome is the same.

In terminal, this is output after npm run build.

This is not a dynamic route.

Location is app/page.jsx So this opens at localhost:3000

import axios from "axios";
import Card from "@/components/Card";

export const revalidate = 15; // seems to have no effect

const AllCards = async () => {
  const url = 'http://localhost:3001/cards';
  const fetchCards = await axios.get(url);
  const cards = fetchCards.data.data;
  return (
    <main>
      <div className='text-3xl font-bold underline text-center mb-4 mt-4'>
        All Cards
      </div>
      <div className='flex flex-wrap justify-center gap-2'>
        {cards.map(c => <Card vanity={c.vanity} art={c.art} id={c.id} />)}
      </div>
    </main>
  );
}

export default AllCards;