It's fundamentally because of verifier's law [0].

Current AI, and in particular RL-based, is already or will soon achieve super human performance on problems that can be - quickly - verified and measured.

So maths, algorithms, etc and well defined bugs fall into that category.

However architectural decision, design, long-term planning where there is little data, no model allowing synthetic data generation, and long iteration cycles are not so much amenable to it.

[0] https://www.jasonwei.net/blog/asymmetry-of-verification-and-...