These tiny dried bodies are used in the Animist practice Kuman Thong
Each such fetus is, in addition to being gruesomely blinged out, worth up to 200,000 Thai baht (the equivalent of $6,300 in U.S. Dollars). That's 50% more than the average per capita income in Thailand, a very significant chunk of money. Kuen was reportedly planning to smuggle the fetuses into Taiwan, where he could resell them for up to a 600% mark-up.
According to the Telegraph, the fetuses are used in "a Buddhist-animist practice known as Kuman Thong that is described in ancient Thai manuscripts." The dried fetuses, decorated with gold leaf, are "kept in shrines within homes or businesses." The practice requires the fetuses of baby boys (snarky comment about how baby girls aren't worth anything in Asia even dead), which have been surgically removed from the womb. They are "dried as black magic incantations were said over the body."
Traditionally, before being roasted in a graveyard in the moonlight by a mage, the fetus would be soaked in a substance "which has the extract of a dead child or a person who died in violent circumstances or an unnatural death." However, this practice has largely been abandoned in the creation of necromantic effigies, due to laws against rendering human fat.
Most people who practice Kuman Thong (which means "golden baby boy") use a small wooden figurine. Adherents believe that if you revere the fetus correctly, it will warn you of danger.
In a kinder, less gruesome spin-off of the practice, the mages adopted the stillborn babies as their own children. (In an animist culture, the spirits of the dead are highly revered.)
Human flesh and dead babies are one of the greatest taboos worldwide. Even cultures which have ritually practiced cannibalism rarely consume the flesh of babies. And as you might expect from the greatest taboo, it is one which holds the greatest power in black magic. Black magic often operates on a sliding scale of taboos, the greater the violation, the greater the effect of the magic.