It's actually pretty hard to design a non-llm system that can detect all the possible variations:
Lights on. Brighter please. Turn on the light. Is there light in here? Turn the light on. Table lamp: on. Does the desk lamp work? It's a bit dim here, anything you can do? More light please. Put the lights on for the next 5 mins. Turn the light on when I come home. Turn all the lights off together. Switch the lights off whenever its daytime or quiet at home unless I say otherwise. etc.
If you don't support every possible way of saying a command, then users will get frustrated because they effectively have to go and learn the magic incantation of words for every possible action, which is very user-unfriendly.