"Smart mines" specifically can be designed so that they're literally incapable of exploding once a deployment timer expires, or a fixed design time limit is reached.

It just makes the mines themselves more expensive - and landmines are very much a "cheap and cheerful" product.

For most autonomous weapons, the situation is even more favorable. Very few things can pack the power to sit for decades waiting for a chance to strike. Dumb landmines only get there by the virtue of being powered by the enemy.