An oven that doesn't heat is just a metal box, right? What is the point.

The reality is that this is common in both gas and electric ovens, but the reasons why it won't heat varies not only by gas and electric oven, but also by brand.

If your toaster is not heating, it is usually due to faulty/damaged components,

selector switches, faulty/burned wiring, or possibly other uncommon causes.

oven grill element
If your gas oven isn't heating, it could be a gas supply, burner, faulty/burnt wiring, or other less common problems.