I am sure LX is worried that CX will also fly to Zurich. Lot of HK residents are very loyal to CX and will for sure prefer CX to LX. Also CX offers connections to the Philippines (two cities), Taiwan (three cities), Australia (4 or 5 cities), southern China which LX does not cover and these are just the likely connections from HKG. Depending on pricing they might offer good deals to SEA or Japan too which will hurt yields for Swiss.

Whilst LX is doing well on SIN that is really only the case in C as the Y fares are usually very cheap. Also as mentioned by others there are people who prefer the night or day flight to Asia and I think it is good to give the consumer a choice.