writing code is the easiest part of software development. Reviewing code is so much more difficult than writing it

A lot of people say this, and I do not doubt that it is fully true in their real experience. But it is not necessarily the only way for things to be.

If more time and effort were put into writing code which is easier to review, the difficulty of writing it would increase and the difficulty of reading it would decrease, flipping that equation. The incentives just aren't like that. It doesn't pay to maximize readability against time spent writing: Not every line will have to be reviewed, and not every line that has to be reviewed will be so complex that readability needs to be perfect to be maintainable.