I've observed that candidates hamstring themselves in ways that seem to me bizarre. Indeed the interview is an unfamiliar situation, so why would you do something like use a language other than one you know well, or code in an environment you don't feel comfortable in? I have had those happen in interviews I conduct so many times! This is for the "front-door" interview, not the on site.
Somewhere around halfway through, when the candidate is floundering and failing on an objectively quite simple problem (I promise it really is that simple), they'll say something like "sorry, I would usually have no trouble doing this in Scala". At the outset I give the option to use their own setup or Coderpad, either one works; they'll choose Coderpad and then halfway through say something about wishing they had such-and-such from their preferred IDE.
I think there is some psychology at play here, where candidates think if they do it on hard mode, it's extra points or something. I really just need them to solve a simple problem so we can be sure they know how to code. The ability to code with both arms tied behind your back is not a signal we're interested in measuring.