Because Tech debt and I reading messy code base never happened in waterfall... The problem is always : features and customer request over bug fixing or design

Because Tech debt and I reading messy code base never happened in waterfall... The problem is always : features and customer request over bug fixing or design fixes. The system, project type does not matter. That's why some PO recommend 10 percent allocation to devops / ops, 10 percent to improving code base . And "no bug survives the Sprint" philosophy. And what is left,is you next feature or customer request.