This depends heavily on your product. There is certain software where I agree with you. But for the usual business CRUD app, why would I need to know my code? It's vastly cheaper to understand code on demand, than digging into every single line of code preemptively.

In my products I definitely take care of architecture, interfaces and data, as they have a high cost of failure. Anything else doesn't matter. If an user finds a rare edge condition, asking an agent to fix it costs less than 10€. Properly reviewing a big PR costs somewhere between 100-1.000€. I would be completely irresponsible to my business to review the code in-depth.