Code dependencies, and how dangerous they can be.
The art of writing code that doesn't build on top of a jenga tower of shit has been lost. It turns every software engineer into a code monkey that, instead of crafting good code, is simply trying to keep the jenga tower from collapsing. Yes, it's faster when getting an MVP up and running, but the quality of apps (and their speed) has gone down drastically over the last 10 years.
...to the point where I no longer enjoy software development, and am actively trying to quit the field.