Cookies are made by whipping butter to white, usually to double its volume. That is to say, the butter is mixed with air, which makes the butter look big.

Then add the eggs, and then add the flour. Flour is low-gluten flour, and the method is to mix it in, just to prevent flour gluten, and the dough after gluten is easy to shrink.

So when baking, the air in the butter escapes and the flour supports the biscuits. Will it retract, then it will be crisp.