Regioselectivity in Ziegler–Natta polymerisation of α-olefins

Why does the Ziegler–Natta polymerization display the regioselectivity shown in the image? Internal nucleophiles (coordinated to the metal) should attack the alkene on the less substituted end, like in the Heck reaction, whereas external nucleophiles should attack the more substituted end (like in the Wacker reaction). Why is this not the case for alkene polymerisation?


[![Regioselectivity in Ziegler–Natta polymerisation of propene](https://i.stack.imgur.com/HJltk.png)](https://i.stack.imgur.com/HJltk.png)


