A lot of this feels like it comes down to the training of the agents to produce code that satisfies the various benchmarks combined with reactions to things which were previously maladaptive. I.e. things which were explicitly trained out of the model in post training. I think there's a lot of missing long term software engineering principles that don't seem to be baked into the way the models tend to write code by default.

I have some speculation that maybe the people doing the model post-training tend to be younger researchers that haven't worked on large complex software systems, so their taste isn't as developed in this regard about what things are important here.

But this is an area that can be steered with appropriate early instructions ("When choosing tradeoffs of implementation, build for long term maintainability and understandability of code over implementing just the exact code necessary to solve the issues. etc. chain of thought often includes information that would have to be repeated in a future agent session, make sure to persist it to code or external docs so that future sessions and user understanding is respected.")

It can also be done as a post-change step with similar effects. And you can use your agents to build this layer into your general modus operandi for dealing with the crimes of generated code. But one of the things that all AI labs should be doing is looking at AGENTS.md on real project as being hard expressions of what failure modes real projects have noticed in models generally. Don't wait fo the bugs to be raised on these things, use express preferences that show that there's a problem. Go trawl github for these in bulk to use for future post-training.