Shared this in another comment, but my luggage was in a locked truck, nothing visible from the back windows. They broke in by smashing the windows, unlocking the door and using the latch to fold the back seats down to expose the trunk.

I regularly leave my backpack with my laptops in it in the front seat of my car in the south US and nothing has ever happened in ten years of doing this.

It's crazy to me other people just live with this. Dramatic action is needed and possible.