The most common accepted answer is some sort of superstimulus theory - modern food is so tasty people find it irresistible.

Why modern food? Doesn't the answer work when modern is replaced by any? Modern food doesn't have to be tastier, it is enough if it is more easily obtained.

almost any "traditional" food seems to taste better than almost any "modern" food

As others have said, this is a very weak argument. First, you have to specify what you mean by modern and traditional food. I suspect that you may subconsciously conflate "traditional" and "tasty", so a specification would be helpful. Then you have to show that your preferences in eating generalise to other people. Finally, explain why modern food was ever invented when it is less tasty than the traditional one. I don't think that people change their eating habits towards less tasty food.