The government cannot craft its policies based only upon the plight of the lowest deciles of the community. It has to look at the whole picture.
If an individual has less than $148,000 in CPF savings at age 55, it's pretty obvious he/she isn't very good at earning money or managing finances. These are the sort that need help in protecting their nest egg hence the minimum sum.
However, all those who capable and prudent will have far more than $148,000 in their CPF upon reaching 55 and they are free to withdraw the money and do as they wish with it.
My cousin who just turned 55 at the end of last year withdrew more than $600,000 and he has opted to leave a further $100,000 which he could have withdrawn in his CPF account because the interest rates are excellent by current world standards. Only the NZD comes close at the moment.