A note: stores throw out unexpired goods all the time.
As for food safety, yup, that’s important. Some goods could be too risky, like raw meat. But so so many goods are processed and stay good long past the expiry.
Expiry does take into account oxygen. Once you open a bag, air gets in and then it could get stale, mold, etc. If it has been sealed in its package the whole time, there was never any (*a lot of) air to start those food-ruining things.