The 737 is fundamentally a 50 year old design and that design assumed some things about pilot proficiency that may not apply today.
When you have pilots in the right hand seat straight out of training school with minimum hours and pilots in the left seat that have the same hours as required to sit in the right seat 40 years ago you could argue that there's a lack of proficiency whether that is in the USA, Europe or anywhere else in the world.
The issue really boils down to the beancounters in the company boards who don't respect the people in their employment or contractors in some cases.