How the disposable private keys are being shared in Lightning Network?
So the question is if it would be unfair to Alice if:


Bob wouldn't reveal his secret information and  
Bob broadcasts the previous commitment transaction


Now, the only case in which Bob would broadcast the previous transaction is if it would have a higher balance for Bob. That would mean that the intention for the channel state update is that Bob would like to pay Alice for something. However, an update of a channel state (balance) is a two-step process:


Alice and Bob exchange the new Commitment Transactions
Alice and Bob invalidate their prior Commitment Transactions (by sending each other a (secret) piece of information)


That means as long as Bob doesn't reveal his secret information to Alice, the channel state is not considered as updated. Therefore it's perfectly fine for Bob to broadcast his previous Commitment Transaction as it represents the current balance. So it wouldn't be unfair to Alice, as from her point of view she hasn't been paid (yet) anyway. Only after she received the secret info from Bob, she would consider the payment as successful.