These questions are an issue in every automated plant. Although you may have a great plant and maintenance engineering department, you can't be sure that it's ready to take on the challenges specific to maintaining a PLC system. Thus, as the person responsible for the system, you become the perfect target when things go wrong. And sometimes, they even call people in other departments too, taking these people away from whatever their doing to come solve a problem that the maintenance department can't fix. All too often, training is overlooked or pushed aside in a plant.
People think that it's either time consuming, expensive, or ineffective.
But this only makes them overworked. Some people in a plant may even think that the maintenance personnel can't benefit from PLC training because they can't understand it. But the reality of the situation is simply that no one has ever taken the time to teach them. This is a time-consuming task. And with all the other work you have to do, you don't have time to be bothered by this as well.