I can only think that, as many have said, the early retirement is down to the problems with breakages. There seems to be two main areas of concern on the Chaffees. One is the fragility of the tracks. Does this mean that K&C have found the current limit of polystone track detailing? I don't know, but the tracks are very nicely detailed, and perhaps there's just not enough polystone to support itself. Or perhaps the use of a different quality polystone.
The second, which seems to be more of a quality control issue, is the gun barrel. I'm aware of quite a few tanks which have arrived with the barrel insecure. This may purely be down to whatever adhesive is used to secure the barrel in to the tank.
The latter is an easy enough fix, the former less so.
I acn only imagine that there ahve been quite a few replacement sets sent to customers, by dealers, which must have a fairly substantial knock on effect for K&C profits. I would guess that it has become not financially viable to keep producing these pieces, with all the labour costs that they entail, when a good chunk of them are going to need replacment, fo no extra income.
That all said, it's one of the best pieces K&C have produced IMHO.
Simon