Can't is an imposition. Can't is a grudgingly accepted duty. "I can't eat this." "I can't do that." "I can't feel what I'm feeling." I'm not allowed. I'm not supposed to. It's an order handed down from faceless authority. You fight against can't.
Don't is an act of self-mastery. Don't is a choice that's already been made. Don't is not a question. There's no decision point, no pros and cons to weigh. It becomes a piece of your identity: this is who you are and how you operate. You fight for don't.