Increasing opportunity cost along a bowed out production possibilies frontier occurs?

Increasing opportunity cost along a bowed-out production possibilities frontier occurs because resources are not perfectly adaptable for the production of different goods. As production shifts from one good to another, the resources that are reallocated are less suited for the new good, leading to a higher cost in terms of the quantity of the other good forgone. This results in a concave shape for the frontier, illustrating that the trade-offs become steeper as more of one good is produced. Consequently, the opportunity cost increases as the economy moves along the frontier.