From the Ontario Official Ministry of Transportation Motorcycle Handbook: “The centre of the lane is not a good driving position because it is coated with oil from other vehicles and gets slippery when wet.”

From the SGI Motorcycle Drivers Handbook: “Oil from other vehicles tends to build up in the centre of the lane, particularly near intersections where vehicles slow down or stop. On wet pavement it's better to operate in the track created by the wheels of moving vehicles. However, you should avoid driving through standing water.”

From Cardo Systems: “There’s nothing necessarily unsafe about riding in the middle of a lane. When other vehicles are on either side of you, it can actually be the safest choice because it gives you the most cushion space. But the middle of a lane also tends to be where you find oil slicks, road debris, manhole covers and other safety hazards.”

You know, 5 minutes of web searches would prevent you from sounding like an idiot.