Changing the business portfolio: between the risk of inertia and the risk of strategic mistake

Large corporations which are stuck into Western mature markets and traditional businesses can hardly grow above 4 to 6% p.a. They do not create value.
Strategically and financially, they need to deeply change their portfolio of businesses and geographies to reposition on high-growth market and to re-allocate resources accordingly. Many groups give up when faced with the difficulty and risks of such a strategy. Why?