It just costs too much and takes way too long.

The technique could not be more simple. Probe the ground with a knife, bayonet, or purpose-built probe, at a shallow angle to avoid pressing on a detonator and, upon contact, use the probe to establish the size and nature of the object in the ground. If it fits the profile of a mine known to be in the field, it is excavated, disarmed, and/or destroyed.

If all mines in the field are known to be metallic, metal detectors can be used to determine where to probe rather than doing exhaustive probing. But the 1000 to 1 false alarm rate experienced with metal detectors in former battlefields means extensive probing is still required.