In the same way they go cheap in computers to compete with dell, hp etc? Companies like Apple (and porsche, bmw, rolex, cartier, prada, any luxury brand) are not about market share, they give up market share when they chose to go for top models only; they aim for profits and they make as much profit with a unit than competitors with 5. In fact you can see how apple with an average of 15-25% share on their markets (phones, computers, tablets) routinely catch 70-80% of the markets profits.
Until apple grow continues at current rates they don't need to fight for market share, also if their competitor get more market than them. Once the markets will stabilize they will be good with their 15-25% market share.