There is demand, but not at the current prices. Its the same as most other countries where eating healthier means more expensive.
Thats why you get a few healthier options around Central and Admiralty, but a lunch will cost you around $100. Whereas a set lunch in a cha chaan teng is just over $50. If you offer me a healthy (and filling, so no just reducing portions) lunch for $50-60, i would take that!