Why does homemade pasta using wholemeal flour break easily as compared to all purpose flour?
This is quite typical for anything made with wholemeal flour. It has all of the wheat berry ground in it, including the hard outer hull. These hull particles tend to cut up the gluten of the dough, resulting in brittle end products. 

The more "rustic" your wholemeal flour is (so larger hull particles), the more pronounced the effect gets. An organic store in my city has a small electric mill for people to buy a pack of grain of their choice and grind it themselves immediately, this makes a flour that is almost impossible to use for dough. Industrially milled flours with smaller particle sizes work better, but not as well as white flours.