iserith
Magic Wordsmith
I am not sure what you mean with the inclusion of "in some circumstances." It is pretty plain in the Strength entry in the PHB that one of the things you can do with Athletics is "jump an unusually long distance." That is a statement of the rules. What I am wondering is why there are no benchmarks for that action.
See "Special Types of Movement" in the Basic Rules, page 64, under the "Jumping" section. You actually can't jump an unusually long distance unless there is something allowing you to do that either in the environment or is otherwise different enough from the standard approach to jumping that a longer or higher jump is achievable. You can't just say "I try to make a Strength check to jump an unusually long distance." The game doesn't work that way. Jump is tied to Strength and Speed, not to ability checks except in some circumstances.