From The Truth About Guns:

A “smart” gun is going to require electronics. Electronics in a firearm are sensitive to all the conditions that the gun is, and more so. An over-heated gun may stop working until it cools. Over-heated electronics will likely need to be replaced. That’s a bit of a problem if you’re trying to use your handgun to defend your home. Same with corrosion from moisture/humidity.
And then there are the G-shocks. Any electronics you hang on a firearm will have to survive thousands of Gs. Repeatedly. Every round fired.
To demonstrate this, take your fancy smart phone. Throw it firmly onto a concrete floor. Does it still work?