Well it makes sense considering they won't be using the half star much. They have 4 good scores(5-3,5), 4 bad scores(2,5), 1 average(3) and 1 broken as shit(0,5).
Having 2,5 be average would mean there were 4 bad scores(05-2) and 5 good scores(3-5) so it's more even this way.