Mutts are only hardy if you breed that mutt from hardy breeds.
A “mutt” is a very broad term. A cold hardy breed is hardier than your general mutt.
And any mutts your breed together for a long time become more closely related, like a breed.
Definitely not for money. There isn’t money in pure breeds.
Pure breeds keep valuable genetics for future generations. Pure breeds give you a consistent and desirable result.
A crossbreed may have strong vigor but any future generations won’t have the same effect. If you didn’t have two pure breeds bred for the traits you want in the first place, you can’t have a crossbreed. It’s not sustainable to constantly introduce new blood or crossbreed. So pure breeds are the solution.