Why the same failure behavior is the right choice for one valve and the wrong choice for another — there is no universally "safer" direction.
Every control valve with a spring-return pneumatic actuator (or a fail-safe electric one) is built to move to a predetermined position the instant it loses its actuating signal, power, or instrument air. That much is universal. What is not universal is which position that should be. Some valves are specified to fail open. Others, right next to them in the same plant, are specified to fail closed. Neither choice is a default or a house style — each one is the answer to a specific question asked about that specific valve: if this valve loses its signal right now and gets stuck wherever it lands, which stuck position does less harm to this process?