For one, you are only "ruining" it for everyone else, as the bank(s) where you had defaulted on your (credit card) loans will now be even more cautious in the future for subsequent applicants. While they may not be able to find you (anymore), depending on how big your debt is, they might find a collection agency motivated to find you. Got a unique enough name where they can Google you? Post in Facebook/Insta much? Gonna come back and visit your family/friends one of these days?
The same goes with back taxes by the way - some countries may blacklist you. Yes I know you're︀ saying goodbye to the country, but as the saying goes, never say never.