Why is store bought frozen food worse than homemade?
I think that at the end of the day, store bought frozen meals aren't per se worse, but rather that the manufacturer needs to appeal to a large, diverse audience of buyers and so their recipes are not tailored to your tastes. Recipes you make at home are often tailored to your taste by the mere fact that you selected the recipe and you know what you like.

They also need to use ingredients that they can get in large quantities, so the individual ingredients may not be the ripest or most flavorful variety (think tomatoes or apples).

Some things frozen at the store are probably better than at home, such as frozen vegetables or sometimes canned tomatoes. They usually have better technology to freeze the vegetables in the most efficient manner that best preserves their important qualities.