Why can't the Chinese hamburger in the old Tongguan rise when it cracks?

I think it's a bun in a Chinese hamburger.

The making method of steamed bread is as follows:

1. Put the flour, yeast, sugar and oil in a large basin.

2. Add water (flour has different water absorption, so it is better to leave a little and need more).

3. Stir with chopsticks before kneading into smooth dough.

4. Cover with plastic wrap and ferment at room temperature to double the size.

5. Take out the dough and exhaust it, divide it into nine small doughs of equal size, and knead them all evenly.

6. Take a small dough, gently flatten it by hand, and then gently roll it into a circle with a rolling pin.

7. Heat the pan, add the dough without oil, slowly bake until both sides are golden, and cover the lid when baking.