Your lack of COVID is certainly largely due to being purposeful and careful, but there's still a component of luck. The only sure-fire way to avoid it is to stay locked up and away from all other humans and things other humans have potentially breathed on. Anything less and there's always a decent chance you'll get it despite your precautions.

Also, you may have gotten it, were asymptomatic, and didn't notice. COVID is fun like that.