Because producing simple and good code is much more important.
It's quite condescending and narrow-minded to say that solving algorithmic problems is thinking, but writing clean and simple code isn't.
Writing readable code is much more than just formatting code and using decent variable names. It's about simplifying your design just enough. Code reviews is not enough to teach someone this.
Why? Teaching people to write readable code happens automatically during code reviews, teaching people how to think is a lot harder.