American accents are often so unintelligible as to need subtitles - I can't watch many Hollywood films without them, especially if the dialogue is quiet or secondary to something happening on-screen.

The issue here of course being that "big film" is made in Hollywood and country-specific film industries are often much smaller and tend to stay far away from big-budget genres, rather than that we should try and find a globally understandable accent. Hollywood having taken over the globe is not really a good thing for anything except economies of scale.