Alphamon_Ouryuken 
"[@SSJGPiccles":](/images/2249912#comment_8851268
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Cozy was taken into the school, shown kindness, and was practically adored by everyone. Yet she still turned on them.
Chrysalis was shown how much more beneficial it was for the changelings if they took the peaceful route since they were no longer endlessly hungry. Yet she wanted to go back to the old ways.
Tirek's brother shared his experiences with the ponies with his brother and tried to get him to change his mind about draining them, and he said no. Even if he was thrown in Tartarus, he had only himself to blame for that. Why should they have given him a chance if he was more than willing to stick to his all the evil ways and seek vengeance just because they defended their home?
They were given reasons to change their way, they just didn't want to.
Cozy pretty much proved she was irredeemable after nearly robbing all of Equestria of their livelihood just for more power. The fact that she was faking it and pretending to be nice just makes it worse since she took advantage of them even though they were nothing but kind to her.
Discord showing remorse over loosing his friendship with Fluttershy was in fact showing that he was actually willing to put some effort into reforming. As well as having some empathy.
Cozy and Tirek had their chances, but they chose to remain evil just because they didn't want to change.
You seem to be missing the point. Just because Reformation is an option doesn't automatically mean that everyone's going to take it, and these three are prime examples of that, they were just too stuck in their own ways to even want to change even when given the chance.
Lord of the Empty Seat
Cozy was taken into the school, shown kindness, and was practically adored by everyone. Yet she still turned on them.
Chrysalis was shown how much more beneficial it was for the changelings if they took the peaceful route since they were no longer endlessly hungry. Yet she wanted to go back to the old ways.
Tirek's brother shared his experiences with the ponies with his brother and tried to get him to change his mind about draining them, and he said no. Even if he was thrown in Tartarus, he had only himself to blame for that. Why should they have given him a chance if he was more than willing to stick to his all the evil ways and seek vengeance just because they defended their home?
They were given reasons to change their way, they just didn't want to.
Cozy pretty much proved she was irredeemable after nearly robbing all of Equestria of their livelihood just for more power. The fact that she was faking it and pretending to be nice just makes it worse since she took advantage of them even though they were nothing but kind to her.
Discord showing remorse over loosing his friendship with Fluttershy was in fact showing that he was actually willing to put some effort into reforming. As well as having some empathy.
Cozy and Tirek had their chances, but they chose to remain evil just because they didn't want to change.
You seem to be missing the point. Just because Reformation is an option doesn't automatically mean that everyone's going to take it, and these three are prime examples of that, they were just too stuck in their own ways to even want to change even when given the chance.