There are so many reasons to keep learning more. But more importantly than anything else, learning allows you to progress. Even if you progress slower than others around you, or if you progress slower than the technology you use, progression is only ever a good thing in learned skills.
From being able to keep up with modern development trends, to being more likely to land your dream job, and simply to better yourself as a developer, learning is one thing you should simply never stop.
If that wasn’t enough to encourage you to keep learning take a look at why other people in the tech space never stop learning!