But that loaf you buy at the store? It'll generally be covered in mold before it gets hard, and that's quite the achievement since it also tends to be more resistant to mold as well! Bread should get hard. This is where a ton of old recipes come from. The Ancient Greeks would dip it in wine for breakfast, Euroland has bread soup/puddings, and even stuff in the US like Thanksgiving stuffings or croutons.
Actually they are not. "Practically" is carrying a lot of weight there. The factory baked cake will have a lot more extraneous ingredients and usually has a larger quantity of sugar and fat. Similar to how restaurant food generally has a lot more salt and fat than home cooked food.
The direct impact of those extra ingredients alone or in combination is not entirely clear at this point, aside from building evidence that people whose diets include more of that seem to be less healthy.
If you stepped inside a food factory you would see how false that statement is
Some stuff is BIO, cream or coconut milk are lower fat version, or carrots are are without residual pesticides. Less salt since we use less salt, and taste buds quickly adjust so its still adequately salty, a better mix of herbs and spices so taste is.. simply better, more refined. We use with much less sugar, the same as for salt above (if you eat sweet stuff sparingly then even mildly sweet stuff tastes amazingly, just don't go from one extreme to another).