I think another factor here is if the reviewer is working on the same code base and the project has a complex environment to set up (e.g., a library compiled with custom flags), then `git stash` may not be enough to checkout the branch and run tests. (I am unfortunately guilty of creating some projects like that myself...) Docker can help with these cases, but not all projects are docker-oriented.

I personally like running the code myself when reviewing, it's just not always practical.