(1) US folks are fragile. They pathologize normal thoughts/behaviors to the point that they never actually learn to live with (or fix) them.
(2) Non-US folks are under-informed. They ignore diagnosable mental health issues to the point that they never get appropriate care for a problem that can be fixed.
It's probably a bit of both. I'm American, and its obvious to me that we are great on some dimensions compared to other countries. E.g., Asbergers-type autism is SO MUCH more understood (and addressed!) in the states. At the same time, "diagnosed with OCD thinking" is a nonsense phrase, as far as I can tell, and is probably going too far.
Therapy & medication are powerful tools; the US is learning to use them more than other places; that might be good or bad for any given person - hard to tell.