the sgh open carparks are designed in the early 70s. At that time, cars are not too many and overcrowding.
today,they failed to expect there is a sharp outburst of owning cars and more sickly Singaporeans
now it is too late to build a giant multi storey cp at sgh because doing so will have to temporary close down the current open carpark for at least 2 years.
That is assuming IF there is any planning being done. I think you give the PAP too much credit for planning. The fact is that the norm today is to see patent in corridors because there are not enough beds, long waiting times at polyclinics, dental care,...