I think it's because they use too much yeast. Sometimes I have bought bread, in very large sizes, but, extremely light. When you open them, that happens.

I also make bread at home. The texture is different, it's much more consistent, I'm not a professional baker, but, my bread never has holes inside.

I use just the right amount of yeast and flour. I spend a kilo of flour to make 3 large and 1 small loaves, all stuffed inside with ham.

I have also made cheese breads, and breads without filling. If you abuse yeast to make a lot of breads with little flour, that happens.