why does sega make sonic game only for nintendo?

i know theres somekind of a agreement that sega will make 3 exclusives game for nintendo consles but what does sega gets from it? im sure they will get alot more money if they made it multi-platform??

Sega sees that a large percentage of Nintendo owners are kids, so they want to appeal to them.

Also, I imagine most kids recognize Sonic's present.

@torenojohn7: That short video was great :)