Some can be born with unevenness, or you can get it from accidents or even pain or postures making you carry your body differently..
Head/shoulder hits or falls may cause c1-c2 misalignment.. can throw the whole body out down the line..
I had a concussion as a teenager- got bucked off horse & hit my head..so that might be a factor for me..minor car accidents, sports ...

uneven body alignment - Google Search