Why do you think it is that many criminals value their dignity over anything else?

I think its for protection. The streets are dangerous and you can't trust anyone. Having dignity makes those around you respect you and it shows those around you that they can count on you. No one is going to go after someone who is well respected because a) they don't want anyone coming after them for going after someone who has a lot of cred and b) they hope that others will show them the same respect back.