I think many are confusing just exactly what an IED is. There is a big difference between a military grade land mine and an IED. An IED is just that, an 'improvised' explosive device. The IRA were masters of this particular device and every time the British found a method of dealing with a device, the IRA would improvise it further to nullify that method, or even make it a trigger action.
The chain tanks were primarily dealing with predictable known types of mechanisms. That is not the case with an IED.