I'm sure that's a part of it, but a bigger reason is probably just that the US has a very large number of manufacturers and most of them are too small to afford the robots this survey is discussing.
I've known many small job shops turning out thousands of parts a day with (automated, but not robotic) WW II surplus equipment; in some cases with the stenciled words "Property of War Department" still visible on the cabinet! Machine tools have lifetimes measured in human generations. There are also many small manufacturers that do everything by hand -- remember that most US small businesses are run part time -- a quick look at my bookmarks shows URLs of a few tiny businesses making just a few thousand units of their product a year.