No such thing as 10k stores that sell relatively niche stuff like a 3900X.
We are talking worldwide. My local computer shop got some in. Not many like 20 units but it's not like only big etailers are getting them. They are just more recognised.
In Japan hundreds of stores got them with people queueing outside for hours prior to launch to get them. There are over 4000 cities in America so if only 1 store in each city got some then that's 40% of my statement there. Of course it's more like there are 2-3 stores in each city dividing up say 200 units. But the premise stands.