> I've been tracking software quality metrics for 3 years

I don’t think you can draw conclusions from that short a period.

As a counterpoint: in the ‘80s and early ‘90s, my brain was almost hardwired to hit the hotkey for “Save” every few seconds while working, even though that could mean applications became unresponsive for seconds, because I didn’t trust the application to not crash while idle.

Yes, part of that is because applications nowadays rarely run out of memory, and likely don’t have code that tries to keep things running in low-memory conditions, but that’s not all of it. A significant part was that applications were buggy. (Indirect) evidence for that is that they also were riddled with security holes.