"Reasons" are merely statements of why something is as it is. Justification isn't used.

"Excuses" try to put an unjustifiably positive (or perhaps a less-negative) slant on the explanation of why something is as it is.

balladeer wrote things like, "So, there was no way I was going to pass my 10+2 (last school year) without cheating and I am lucky that I somehow managed to cheat." and, "I wish I could have cheated better so that the meagre Chemistry score couldn't bring my total % to around 75."

To me, those appear to try to make it sound like the cheating was somehow okay, or even a good thing, even though this cheating was apparently covering up a lack of ability. They aren't merely saying why cheating was used; they try to make it sound acceptable, when it clearly isn't.