Why don't some Italian tomato sauces and pastes use citric acid?
Citric acid is added when the PH of the overall product is too high. Most of the time a product with pure tomatoes doesn't need any help with PH as the tomatoes should be acidic enough, when you see citric acid added you will usually see water added as well in some form. Water is added to bulk up the product and make it cheaper, some companies add tomato juice instead of water as it looks better on the labeling , but at the end of the day tomato juice is just flavored water. Water increases the overall PH level, so you have to bring it back up. 

When you don't see citric acid in a can of tomatoes or a tomato product it's usually a sign that they are really good quality.