This is something I have wondered about before: whether AIs are more likely to give wrong answers when you ask a stupid question instead of a sensible one. Speaking personally, I often cannot resist the temptation to give reductio-ad-absurdum answers to particularly ridiculous questions.
If 30% of humans on the internet can't be bothered to make an effort to answer stupid questions correctly, then one would expect AIs to replicate this behaviour. And if humans on the internet sometimes provide sarcastic answers when presented with ridiculous questions, one would expect AIs to replicate this behavior as well.
So you really cannot say they have no incentive to do so. The incentive they have is that they get rewarded for replicating human behaviour.
If 30% of humans on the internet can't be bothered to make an effort to answer stupid questions correctly, then one would expect AIs to replicate this behaviour. And if humans on the internet sometimes provide sarcastic answers when presented with ridiculous questions, one would expect AIs to replicate this behavior as well.
So you really cannot say they have no incentive to do so. The incentive they have is that they get rewarded for replicating human behaviour.