No job is ever phrased as needing a code-monkey and no one wants to think of themselves as a primate doing a very specific task.

Why would you put out ads for senior engineers when you'll make them perform code monkey tasks?

Every job has random overhead and your productivity is boosted quite a lot by already being familiar with some random bullshit problem like "don't configure your test environment this way or you'll run out of file handles after a day or two." Hiring more experienced people means fewer delays due to issues like that, even for boring "code-monkey" work.