With snowboarding specific stuff it's mostly hip and low back stuff, because most boots prevent a ton of dorsiflexion.
Basically if you cant do a good squat, you're at a much higher risk for injuring yourself snowboarding, in terms of an overuse injury
While I don't disagree that your hip/feet/lower back can cause knee pain, I think you're overly applying your own experience to this situation. Your personal situation does not equal the situation for everyone and how your body reacts does not mean it's evidence that everyone's body will react the same way.
There are a lot of people here who can squat just fine and actively stay in great shape and still have knee pain due to wear and tear from injuries and impacts.