This is a very interesting question I took home after I visited the Arcaeological museum of Paestum.
The story preceding it is this: antique Romans were, as said in the title, very closefisted. Or maybe they were simply rationally thinking. They adored statues (learned it by previous Greek culture -that is why there are many copies from Greek originals that existed at the times of Romans else) but often had not enough money to buy them for every occasion. So, they adopted a simple strategy: they changed the heads of the statues. The cost of the only head is clearly much more reasonable. Specially, if one lives in the times when the Emperors change faster than the seasons.
Here, on these two photos, you can see clearly what I'm speaking about. You can see that even the arms could be easily changed if necessary.
My question is about this next statue. It's obvious that the head was broken, the arms and legs broken, too. But one part was clearly replaceble. It's evident even if you see on the photo.
Now, could you explain me: why had they to change THIS part?