It’s funny what happens to your skills when you work for years on one main type of project, with one main toolset. You get really good, and super fast at doing that thing. However, your skills in the greater scope of your industry start to get out of date.
And what if you have scaled back your time for professional tasks, maybe due to a second job, or having kids, or health issues? The problem of skill stagnation gets worse. Then add a work-from-home situation with less time for interacting with peers and, well, you can guess. You become a dinosaur in your industry.
EDIT! I decided to take what was a long blog post, and turn it into an entire blog about keeping your development skills up to date, and share my own learning processes and resources. Check it out here: Develasaurus.com.