He didn't know they got to the bell, he sent them off to learn to work together because if twilight defeats them together she'll gain the most confidence. And he likely didn't know they could use a bell seeing as they had to break in and get a book to learn. Basically it falls back to what we talked about earlier. Discord established flaw of arrogance.
[@Mediocre-Grimm](/forums/pony/topics/ron-the-death-eater-discord-s9-finale?post_id=5146180#post_5146180)
He didn't know they got to the bell, he sent them off to learn to work together because if twilight defeats them together she'll gain the most confidence. And he likely didn't know they could use a bell seeing as they had to break in and get a book to learn. Basically it falls back to what we talked about earlier. Discord established flaw of arrogance.
Discord get so many second chances because he grows each time and is genuinely remorseful. Rome wasn't made in a day. Considering hes ok with starlight and tempest he seems to be fine with it like everyone else if they actually show they wanna change.