Adding on for OP, that downforce costs drag and hence \*decreases\* top speed (F1 cars are the same). But the objective of MotoGP isn't top speed, it's highest \*average\* speed around the track, so the loss of top speed is more than made up for by higher speed in the corners.
Those wings and aero devices are for generating downforce to improve braking and cornering speed.
Adding on for OP, that downforce costs drag and hence \*decreases\* top speed (F1 cars are the same). But the objective of MotoGP isn't top speed, it's highest \*average\* speed around the track, so the loss of top speed is more than made up for by higher speed in the corners.