One thing that might be taken into account is the delay between ordering a plane, and the delivery (can take up to 10 years), so 1.5 years and 139$ million is worth investing into, to keep revenue flowing earlier.
A new A380 is more expensive (rule of thumb half of official list price, so about $220 million), and airlines were not talking about retiring A380s yet at the time. So it even made economic sense.
The plane has since had a cabin upgrade and is still expected to operate at least until 2028. It’s operating SIN-LHR right now as I write this, currently flying over Azerbaijan.