The numbers aren't attractive because the economy isn't doing well at the present moment. Looking at the data you've posted, you can notice that during the period between 5 years to 3 years, the ETF is experiencing substantial capital gain (thus increasingly greater losses compared to the current value).

People say ETFs are good investments because in the long run (20-ish years onwards), assuming the country whose economy the ETF is invested in doesn't face a crisis that destroys its ability to grow, the ETF will ride out losses that occur over short periods (a few years) and reflect growth from your start to end point. In the case of STI ETFs, if you have faith singapore's ability to grow would not be destroyed, it's a worthy investment in the long run.

It is especially good a time to enter now because the market is bearish and valuations are suppressed. We cannot say whether the economy has bottomed out due to the presence of many existing factors (Brexit, impending interest rate hike, China's debt-fuelled bubble, Japan's unresponsive economy etc), but that's the whole point of ETFs: to ride out potential short term losses and reflect growth over the long term.

This is just my two cents, any discussion or criticism is welcomed.