Why are the Big Bikes in MOTOGp are 800cc's? Why not 900cc's?

Question

Why are the Big Bikes in MOTOGp are 800cc's? Why not 900cc's?

Answer 1

They all came to the conclusion they could not use the power.

the bikes could not put the power down on the track without spinning up.  the smaller 800s use less power but get more grip, allowing for more acceleration than the bigger 990s they also go a lot quicker around corners. giving faster lap times than the 990s.  just as Wiggysan points out.

Answer 2

They used to be 990 cc but they were slower then the current breed of 800cc bikes.

800 seems to be a great balance of power / corner speed.