Location is a huge difference. Hong Kong is right at the door step of China, the next explosion of market of air travel. Combined with Dragon Air that Cathay Pacific simply has too many options for SIA to effectively compete. Also, for an Asian Airline CX has a huge market in North America, and as Europe is slowing down that hurts SIA greatly.

Ultimately, SIA can't beat the location and convenience of Hong Kong.

There is still a way for SIA thought. Taiwan always want to be Singapore's best friend. Singapore Government can really try to twist Taiwan's arm and exchange friendship and more bilateral cooperation in return get Taiwan to allowed TPE to be SIA's "sub-hub." I am no expert in international airline laws but if this is allowed, say if SIA can offer something like this: JFK-TPE-PVG/PEK/CAN, etc. Then it can seriously challenge CX. Otherwise, dress those FAs as sexy as they want, have better hardware, better IFE, better food, it won't matter.... Can a foreign airline operates a hub out of another foreign nation?