Amber is a unique gemstone in that it’s originally organic.

Well, and pearl. And jet. And coral.

There's a fair amount of editorialization in the Discover summary. The original study dedicates about two paragraphs to "why":

n this context, the amber equivalents may have been: i) a substitute to meet the high demand for that raw material which was impossible to satisfy by the suppliers; ii) a low-cost product with the same social function as amber used by segments of society that were not wealthy enough to acquire the real product; iii) products used by middlemen to cheat the purchasers. The last possibility might be the case in Cova del Gegant where the four resin-covered beads were found together with two beads of Sicilian amber [2] of very similar size and shape. This supports the idea that the resin-covered beads can be regarded as amber equivalents as there are no apparent differences between them and they form a homogeneous and coherent group of adornments de visu.

The identification of those two beads as Sicilian amber [2] poses a problem regarding the interaction networks of the Bronze Age groups. Unlike the situation in the third millennium BC when most of the amber in the Iberian Peninsula came from Sicily, most of the second millennium BC beads came from the Baltic region [2]. At that time, the sources of Sicilian amber were exhausted, and the central and eastern Mediterranean were the poles of attraction for most of the exotic products that were circulating in Europe and the Mediterranean. Thus, the epicentre of exchange networks moved towards the central and eastern Mediterranean while the source of the materials changed. This would have led to a lack of supply in the Iberian Peninsula, which would be reached by very little amber, mostly from the Baltic. It is therefore significant that Sicilian amber reached Cova del Gegant, possibly some of the last Sicilian batches, together with other elements clearly of a southern origin, such as the gold tutuli, probably through exchange networks that had been operative in the previous millennium. Again, the presence of the two gold tutuli in the mortuary level shows that the inhumed individuals had been able to acquire exotic elements. Therefore, as no doubts can be harboured about the wealth of the individuals, it is possible that the middlemen who supplied the elite with their prestige items, in a situation of shortages in supplies, high demand, exhaustion of traditional sources and the inability to compete with the central and eastern Mediterranean decided to create the amber-equivalent beads. However, it is also possible that, owing to the difficult access to this prestigious raw material, the two Sicilian amber beads were re-used and come from earlier burials, and the resin-covered beads were produced locally to increase the number of items for display.

For what it's worth, the faking of amber has as long a tradition as any scammery in jewelry. The techniques aren't advanced; you take some not-quite-amber tree sap, melt it down and let it harden. A 600-year historical record ain't a 4000-year historical record though so that's pretty cool.