I blame the school grading system for it. 70% and below is already a failing grade in many courses. So by extension anything that gets rated 7 or below is asscoiated with failure.
I am not from the US, so I don't know how long this grading system has been in use there but here in Central Eruope that's a rather new thing. That's why a 5/10 didn't feel as bad 20 years ago while today a 7/10 feels worse.