That may be your perception but in fact Hangsen production facilities put most small juice makers (USA/R.O.W) to shame.
There is a you-tube video out there somewhere showing their labs/production facilities.
Chances are that some of the juice you buy in USA may well contain Chinese made base materials/nicotine.
I am far from a China apologist and share the concerns of many over toothpaste/dogfood/kids toys etc but in common with many on ECF have been happily vaping Hangsen liquids for over a year - of course a few of them have been yuk! (to my taste) but that was due to my choice of flavouring, not the juice itself !
I have found a few of the US made Halo juices yuk! also, again to my taste, and some of them terrific.