Q. Why does Al HaNissim say we are not allowed to enjoy the Chanukah lights?
The rule is quite different on Shabbat, when we may not say a blessing over the lights unless we derive benefit from them. Rashi says (Shab. 23b) that they are there to ensure that the people in the house do not need to sit in the dark. The same is true with the Havdalah candle: we may not say a blessing over it unless we derive benefit from the light (Shulchan Aruch, Orach Chayyim 298:4).
The Chanukah lights, on the other hand, are not meant to dispel the darkness, but to convey a meaning – that in every generation we must stand up for our values even against the mores of the time.