The rotation of the engine makes any ski naturally want to turn in the opposite direction of the engine rotation.
As the engine spins, it naturally makes the ski lean to one side slightly. It's a fascinating phenomenon - lots of "phun" physics involved. The same thing can be felt on my old two stroke Sea Doos - they like to turn to one side a little bit more than the other.
Imagine revving an old muscle car with a big engine. The car twists a little bit on it's suspension as the engine revvs up. More torque is more movement side to side. You can also watch this phenomenon in semi trucks as they are under heavy load. You can see the cab twisting to the side a bit as they change gears - especially when starting out.
Keep in mind that this effect should be fairly slight. If it's really pulling to one side or another then you likely have a steering misalignment.
It's all about torque and angular momentum:
https://www.khanacademy.org/science/physics/torque-angular-momentum
Never thought I'd be posting a link to a physics lesson on this forum...