Because the goal is still an hour, but there are different levels of failing. A simple binary "pass/fail" means the record shows the same difference between lying in bed all day Vs running a marathon and walking 59 minutes Vs 61. If I'm 2 grams above my goal weight at Christmas is that a simple "fail"?
You are right that setting a goal aligned with what you want to change is the important question, but you want you achieve may not well fit into a clear pass/fail.