Whats The Big Deal With PlaKids?

You know, this is an aspect of the hobby that I would truly like to understand better. To me, PlaKids are a sort of cute, charming ancillary of the Plarail line but I don't personally use the few I have.

I guess there's some deep nostalgia among adult Japanese collectors combined with a restricted supply and enough disposable income to make aftermarket prices rapidly spike.