Why does Numista value many circulating coins at less than their face value?

An example is a  1993 Hong Kong $5 coin; but there are numerous other examples. This is a currently circulating coin, and can be spent in Hong Kong to buy  '5 Hong Kong dollars’ worth of … whatever. This = 0.97 Australian dollars. Yet Numista states that the value of this coin, in good condition, is only 0.42 Australian dollars (less than half of its current face value). How can this be?

The values are generated from users buying prices and auctions. You also can often get run of the mill foreign standard circulation coins for less then face because they are literally worthless unless you physically go to where they have a monetary value or sell them off to somebody who will go there etc.. There is also the possibility of exchange rate differences, the values are all stored as Euro in the database and if you get a stark breakout of a currency against the Euro this can sometimes distort values too.