Your team may not have enough developers allocatable to refactoring tasks. They may already be busy with important functionality, and cannot afford getting distracted, just to update language or framework versions, adopt to new clean coding style. Have you been putting of unit test coverage? Or maybe you just need to review your code architecture to see how well it fits current standards. I can become part of your team to help continuously refactor your code and participate in cod review process to enforce a direction in code quality.
Some Examples of modernizations and migrations:
Zend Framework to Zend Expressive, Laminas, Mezzio
Adding Unit Tests coverage
Asp.Net Core 2.x to Asp.Net Core 3.1, 5.0+
JQuery, React to Веб Компоненты и Blazor
Intorucing MVC architecture