I don't think you can compare American Bass to Sundown. Of the 14 or so lines that American Bass sells 9 or 10 of them are less than $200. The E series by sundown is literally the only non-shallow sub $200 sub they make (Sundown and American Bass are targeting 2 different types of buyers).
Completely different markets. American Bass's target is the sub $200 range (same with brands like CT Sound and Skar). American Bass of course has a longer history, more revisions, and more R&D compared to those other 2 brands so there often the more "safe" choice.
The actual "made in USA" tag is pretty rare for subwoofers. MMATS entire sub catalog above 200 dollars and the 1500 and up series from Digital Designs are the only 2 semi popular companies I know of that have it. It's usually "made in china", "assembled in usa" (all chinese parts but put together here), or "built in USA" (assembled here with a mixture of domestic and non-domestic parts).