Well, the 'made in China' angle may be relatively new - and IMO goes back about 3-4 years during the gypsum shortage in the US brought about by the hurricanes...- but it should surprise no-one that China can produce pretty well anything at a fraction of the cost that North Americans can. A gypsum plant is normally located close to mines so that transportation costs are kept to a minimum but that doesn't mean that it easy to put up a drywall plant. If you've ever seen a drywall plant running at full speed, you'd be in for a treat...
That board comes out at about 60 miles per hour, out of a puffing and wheezing machine that's about a football field in length. One mistake or one accident - and by the time the machine shuts down - there's 10 miles of rubbish gyproc hurled against a wall somewhere. We had 3 gyproc plants up here back in the '80s going full tilt day and night.
"Gypsum" is basically calcium sulphate; calcium sulphate contains sulphur; under certain conditions, sulphur can produce hydrogen sulphide which has a classic rotten egg smell. Hydrogen sulphide is corrosive to metals and turns metals behind a wall, say plumbing, black and weaker. In the long run this could cause problems.
Even discarded gypum panels can decompose to give off that rotten egg smell and since there was so much rubbish produced back then, it may not be surprising there's more rotten egg smell around.
But whether the rotten egg smell can be only attributable to "made-in-China" gyproc or not, I don't know. :huh: