The virus is relatively minor in most people so a travel ban would be a disproportionate response.
Add to that the fact that the USA is huge and the number of confirmed cases vs the total population is far lower than that of Singapore.
If you look at the real time map you'll see that there are HUGE states such as Texas that have only 76 cases which works out to a far lower infection rate than Singapore's
Singaporeans pose a greater threat to the world than the Americans do based upon the current data. This also means that you are far more likely to catch the coronavirus from your fellow Singaporean than from someone that has arrived from the USA.
Never forget what's the true name of the coronavirus (COVID-19): 武汉肺炎... translated as 'Wuhan pneumonia'.
Second massive outbreak in China soon:
1) The rural morons who go back to the cities to resume work, and
2) The brainwashed Tiongs living outside China who believe the situation back in China is much safer than in other countries, so they went back home.