Failure To Boot/Verify Disk
Your partition map and your file system are two different things; kind of like the difference between a car and it's driver.  In your case, the "car" may be fine, but the "driver" is impaired, so you're not going anywhere (likewise, if the car is totaled, it's unlikely the driver is also fairing poorly).


File systems get corrupted for any number of reasons.  You can easily fix this with a reinstall of macOS; from Time Machine is the best method.
It's possible that your SSD is failing.  In that case, you can replace it with another and have your MBA back up and running.


Finally, running Disk Utility "regularly" doesn't do anything to prevent failures like this.  It's a much better practice to regularly do backups.