That's on purpose. Used to be they only tested straight-on crashes. Of course this ment that car manufacturers only optimized for that situation. In the real world you're rarely aiming squarely for the front of the other car though, so those sorts of crashes were rather a lot more lethal until crash testing started taking them into account.

It's also generally just a harder crash for a car to deal with, so it makes sense to use in a comparison like this.

Unfortunately they may be over-optimizing... https://danluu.com/car-safety/ discusses "gaming" the tests. Maybe protect the driver more at the passenger's expense.

What's that quote about metrics and goals again?

Crash testing will need to continually get updated to avoid manufacturers being able to target the tests too much.

Most common type of collision IIRC

It also distributes stress between the "safety cage" around the passengers and the structures on the side of the car. Modern cars respond pretty well to a perfect head-on collision but things get messy with an offset crash.

Such that the drivers crash into each other, and not into the empty passenger seat of the other car.