Code has a Complexification Factor.

That is, how many orders of magnitude more complex is it than it would need to be if the world paused and seasoned engineers had 3 years to work on it?

Agents can make it 10x, or 100x, or even 1000x more complex than it "should" be.

Humans give up if a slog is too painful; agents will happily continue until their human tells them to stop.

Human ICs will complain about a slog to their manager.

Agents rarely will bother complaining about a slog.