Comment by causal
It's even more subtle than that. Things just start decaying when talent leaves- you often can't trace it to a single engineer or piece of knowledge that's lost. You'll find reasons why things broke- but you won't see the myriad ways a more talented pool of developers would have prevented it from ever breaking in the first place.
This is what's happening in my org, talented people was leaving consistently (5-6/month), things are currently maintained with skeleton crews -- the ones that are maintained, the rest are accidents waiting to happen.
Quality inertia is what's preventing stuff from crashing down instantly, but it'll eventually be the case. It's just a matter of when the last guy that's worth their role leaves.
Most "SDEs" attracted by past big money have below-minimum reading skills, can't write code, can't troubleshoot, can't debug anything even if they life depends on it. They were hired to form a particular structure for the manager two levels above to be promoted.