Pitstops or yeah nah?

How come the motogp teams dont do pitstops? Chance to fuel up or swap bikes etc would surely mean that a longer race is possible and be more entertaining & dramatic?

How come the motogp teams dont do pitstops? Chance to fuel up or swap bikes etc would surely mean that a longer race is possible and be more entertaining & dramatic? http://ifttt.com/images/no_image_card.png