Sierra, Silverado, Avalanche, Yukon corroded brake lines

My son is a Mechanic, last year he was working at a Small Independent shop in the Baltimore MD area, He said they were getting a lot of these in mainly brake lines. One was so bad he said the brake baking plates were rusted out and they had to replace them also. The older trucks did not have this issue because I have owned 4 GM trucks in the 91-95 range and none of these had this type of issue.