I think you just have to look at what the two stories tell you.
The upward trender started off really poorly, learned their lesson, and started performing much better (must have been 3.8+ to get it up to where it is). That person is capable of self-assessment, adjustment, and good performance.
The person who stays at 3.4 is either unable to judge their performance, indifferent to their performance, or unable to perform better. Not that a 3.4 is bad, but you see how the two differ.