Maybe because american hosts are better, i don't know.
If you play GTA V, when i used to, i could play in chinese servers/australian ones without ANY LAG, i mean:
Without getting laggy while entering at cars, etc, but it's host related, even if a Chinese plays on my server, if his internet is good, he's gonna be fine.
But if his internet is bad, he gets fucked up, even though the host is good, itself.
I'm just giving examples, i can't explain nor to help you, sadly.