I had a fingerprint scanner on an old phone and it would fail if there was a tiny amount of dirt or liquid on my finger or on the scanner. It's not big deal to have it fail on a phone, it's just a few seconds of inconvenience putting in a passcode instead. On a firearm, that's a critical safety defect. When it comes to safe storage, there are plenty of better options like a safe, a cable/trigger lock, or for carrying, a retention holster (standard for law enforcement).