Internal Developer Advocacy is crucial for improving DevEx as it enables organizations to tap into the wisdom and talent of their community, break down silos with communities of practice and knowledge sharing, and communicate culture change effectively. This approach helps in making developers successful by ensuring greater productivity, shared best practices, and better developer experiences. By focusing on internal developer relations, organizations can foster a culture where developers are empowered to take full control not just for writing code but also for shipping and running of the software they create.