Chris, a number of others have covered the China made issue pretty well, I will address the "in stock" issue.
I feel your pain, I once ran a train department in a hobby shop and back in the day inventory was king - you cannot sell what you don't have - or so it would seem.
A lot of factors have come together making it very hard for retailers or even manufacturers to keep big inventories.
Retailers once enjoyed larger markups, which allowed them to keep money tied up in inventory. Today, everybody wants a discount.......
Manufacturers have provided us with increased detail, accuracy, and variety. This in combination with the simple fact about markups, makes it even harder for retailers, online or otherwise, to have big inventories.
So the manufacturers have cut the size of each production batch, and large percentages of each run are spoken for before they are even produced.
It is my understanding that Bowser and Intermountain still do their injecton molding here, and package kits here, but RTR items are assembled overseas.
EPA regulations on painting and indirect labor costs (taxes, health insurance, unemployment coverage) are the primary reasons RTR model trains are not made in the USA.
When Athearn first got back into RTR, they too did the injection molding here and shipped parts to China for assembly. They have since discontinued all USA manufacturing. There is a long standing rumor that Athearn kept much of their original tooling here in case things go south in China, allowing the Chinnese to duplicate the tooling to produce the exact same items. Not sure how true that is, but given how easy it is today to make some of this tooling, it is quite possible.
Fact is, the US economy will simply not allow workers to work at pay levels that would be market effective for these products. Now if we had a different type of tax structure, and did not demand 1/4 of the productivity of even low paid workers in tax payments, maybe more things could be made here, and workers could still take home a reasonable wage?
But the unwillingness or inablity of current model consumers to pay reasonable markups prevents manufacturers and retailers form keeping large inventories in any case.
And one more thing about the choices the maufacturers make. In 1968, when I became an active model railroader, we only had about 100 years of railroad history to choose our modeling from.
Today, we have now have about 150 years of railroad history to choose from. So it is very likely that the demand for any one product, like a GLa hopper car, is actually much smaller than the demand for a similar product when Athearn introduced their 34' twin hoppers in the 70's.
Railroad history has grown faster than the population, and faster than the total number of modelers for sure, and a much wider selection of product has been made in the last 20-25 years. Making the demand for any one product MUCH smaller.
Again, combine all that with my first point, smaller markups, make it harder for retailers to invest in large standing inventories.........