Its a niche market comprising of few hundred VWs. And among those few hundred cars, only dozens are with the true enthusiasts who keep their hobby cars the way they should be kept, with all the right (and at the same time expensive) parts on them.
The parts as can be seen are rather of high prices as compared to any other auto maker's parts line thus the investment in say one container of tiny bits could be way over many millions of rupees at a single import. Since there are literally a few who really spend big bucks on their VWs the importers feel their huge sums are blocked in parts which no one apparently wants to buy. As a result of months & years of blockade of investment, eventually the importers have shifted their capitals to other auto maker's parts lines, utterly resulting in total wash out of "keep on road" parts from the market unleashing a havoc for those who want to spend to keep their VWs in the best nick.
Having said that, there has been a steep inclination of awareness of vintages and thus VWs in the society in last couple of years, with more and more people being attracted to car shows after media blasts. That too has resulted in a sudden rise of demand of both, the vintage cars as well as the parts which keep those vintages on road.
I hope I have been able to explain how it should have been.