Because the implementation should be familiar to most devs, which makes it easier to see what kind of language you're dealing with.

Binary sort would be another candidate for me, but people get it wrong in subtle ways and not every language does array updates.

Your examples don't make much sense to me. A web app using what framework? What does that say about the language? CLI apps could work if you could find one that people recognize and that's small enough for an example.