A counter rotating engine has different parts compared to the normally rotating model. This means that you have to maintain spares for two different engines ie can't keep a particlar spare part that could be used on either engine. This costs more for little or no gain in safety.
Performance & handling limits are based on the worst case failure ie the critical engine. As long as the a/c is operated within its envelope then a failure of the non-critical engine could give you a slight 'bonus' or buffer over & above critical engine performance & handling limits.