Some details and the same in English. Turns out this route is only used if you set the starting point to the other half of the nearest 22 building left of the spot. If you move the starting point to the further half of the nearest 22 building it already takes the route going around Makslahdenpolku adding a few hundred meters to the route to Laajalahden koulu (or any of the closest bus stops like Kirvunristi). In the route through Makslahdenpolku it still uses the walking routes through the same small forest as in the highlighted spot. So clearly it is not even trying to avoid crossing the forest but somehow just doesn't like this particular route. 