It’s not that they don’t know about us.
We are just a quarantined planet.
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This is far more likely. Aliens probably see the inhabitants of this planet as extremely dangerous. The way we might see a tribe of primitive headhunters.
For me, it’s the sin issue. The natural consequences of sin must become undeniable, which may include the conditions to which we might extinguish ourselves.
If God were to allow advanced races to make an appearances, they could save us from continuing down the path of sin. If we were saved from our sins, then man would not face the full consequences of sin. If that were to happen, we would have an out as to why sin cannot be considered that bad and we might continue.
However, if we were allowed to continue down the path of sin until we have extinguished ourselves. Whether because of AI or a too polluted environment or disease from bad chocies, then it becomes undeniable and we will be more ready to be completely obedient even on the smallest of sins because we know what might happen now.