[Oyk]

Yes you hit the nail. 
Almost all Malaysian are car owner. Who need a train to travel within Malaysia? 

The hundred thousands of Causeway way commuters are Malaysian or Ex Malaysian, going back to JB. Working in Singapore. Who need the HSR? 

The main objective of HSR for Malaysian politicians, is to build up the stations vicinity infrastructure. Generating GDP. 

Not really for transportation needs.

Therefore Singapore's participation in Malaysia HSR is not the main concern of the project. Other than being a investment point of view, for Foreign Investors interest. 

To Singapore, we are just a last station, similarly to current existing train system. Not much expectation from Malaysia's HSR. Probably more towards enhancing diplomacy with our neighbours. If it is not too costly for our tiny island nation.

They hope to get a slice of the business we have here by making the journey from Singapore to KL faster. The stops in between are a waste of money to build and a waste of everybody's time to wait for probably no passengers or just a handful or so.

Of course there's also the ego factor, the same reason for building the Petronas Twin Towers. When the country is broke and its currency is losing value, it does not stand to reason to spend on such lofty projects instead of on alleviating poverty. 

I don't wish to sound arrogant or patronizing but just look at KL. It's the capital of the country but looks no better than a tier 3 city in China. Building a HSR is like living in a house with old broken floor tiles, walls which are stained with mold and dirt, toilet bowls which are chipped while parking a Lamborghini or Maserati downstairs to show off.