In the article one of the scholars posits that the restorers tend to go for the most vivid and saturated versions of whichever colors they detect.

We should also note that many of these statues were placed outdoors. Colors might seem bright and garish in gallery lighting against muted white backgrounds but wouldn't pop quite so much under bright sunlight in the middle of a public square, especially once they develop a patina of dust and the sun starts bleaching them out (which would take no time at all under the Greek sun).