They do care. It's a matter of priority in the moment when they commit violence.
The priority system in the brain goes something like this:
1. Get revenge on the person who they feel wronged them
2. Look out for for self-interest (avoid prison, etc.)
Then, after #1 is achieved, the priority system looks like this:
1. Look out for self-interest (avoid prison, etc.)
and they're like... oh shit.
In Masvidal's case, he even prioritized his reputation above avoiding prison though. Bragged about it on social media and so on.