I’m guessing its to mimic the command they will see on the AP CSP exam which uses AP CSP Pseudocode
Code.org added a lot of functions that aren’t very useful. They also have timedLoop which is a copy of setInterval but with small changes in the way you use them. Sometimes they’re a little bit better and have some more ways you can use them in. I don’t know about appendItem.
appendItem() doesn’t require a discussion about using methods on objects.