I would go one step further: why would the question be irrelevant for a janitor? Let's say you search for a janitor for a high school. You have three good candidates. One just applied randomly. One lives just around the corner, and wanted to find a workplace where he would not have to drive for hours. The third one lives far away but loves interacting with teenagers: for instance, he is a karate instructor in his spare time.

Feels relevant to me. You can apply for a janitor job in a lot of places, so it cannot hurt to ask whether there is a reason to choose this particular one. As other said, just saying "I need a job and this fits my profile" should be an acceptable option.

Let's not pretend that question is what will make or break the interview. I always see it more as an ice breaker to get the discussion started.