In fact, they often just build a bunker and do a controlled detonation - the bunker directs the explosion forces upwards, where they don't harm anything. Not sure why they decided to defuse this one.
When it is easy, they defuse it. But usually it is all rust, so controlled demolition is the preferred way to go and usually always done, unless it is hard because of sensible surroundings. But then the bomb gets transported.
