MADAGASCAR: How (why) did Austronesians come to Madagascar?

The eastward migration - taking place around the year 500, it is thought - is a mystery:

'One can only assume that the island of Madagascar played an important role in trade, particularly that of spice trade (especially the cinnamon) and timber between Southeast Asia and Middle East, directly or through the African coast and Madagascar.'

https://en.wikipedia.org/wiki/History_of_Madagascar#First_inhabitants_and_settlements_(500_BCE%E2%80%93700_CE)

Source: Wikipedia