You have missed an important step: Once the productivity goes down because complexity spikes, the original developers flee the company, if their cv allows them.

You have missed an important step: Once the productivity goes down because complexity spikes, the original developers flee the company, if their cv allows them. They are then replaced by new hires that got fed lies at their job interviews. The managers had to lie to get new developers for their shitty codebase. That's where development time and costs double while quality is bottom of the barrel.