This is a reasonable programming language design choice.

CMake actual gotchas I dislike enough to avoid it as much as possible include defaulting to cached information, even after I make changes, and preferring "smart", opaque and even hard to track down scripts to explicit user input. It seems optimized for cleverness and conciseness, at the expense of reliability and required user effort.

This is actually a useful comment and points out something I didn't know (about how the CMake if statement resolves variables).