Airport absurdity

Please explain to me why, once you've gotten through airport security and surrendered all your liquids and gels, you are still prevented from purchasing liquids (e.g., water) and gels (e.g., toothpaste) inside the secure area to carry on the plane? That's ridiculous. So, now you have to be searched twice, once when coming into the secure area and again when you get on the plane.

Absurd.

Since Thursday, screeners have searched more carry-on luggage by hand. They also randomly checked passengers at airport gates to make sure that they hadn't bought toothpaste or drinks at airport shops after going through a security checkpoint.