This is because bread that is not only “made with 100% whole wheat” (which just means it contains SOME 100%-whole-wheat flour!) but is made with ONLY whole wheat flour (plus any other whole grains) doesn’t rise very well.

I don’t know anything about baking bread so I can’t tell you how they do it, but in my country (the Netherlands) whole grain bread has to be made from 100% whole grain flour by law. If you add any other kind of flour you cannot sell it as whole grain. There is plenty of delicious whole grain bread for sale both in supermarkets and bakeries.