I'm a freelance writer, which means that I spend a lot of my time researching and writing content about topics that can be very interesting. They can also be very dry. While I love my work and the challenges that it forces me to face, there is a distinct difference between the type of creativity that writing for business clients requires and the kind of creativity that writing for myself requires. It's a totally different headspace.
Yet, I find that if I don't make time to write for pleasure - to create stories with no monetary value attached to them - then my "day job" writing evaporates into uninspired, jargon-loaded content that may meet a list of requirements but doesn't really represent the best that I have to offer.
I've found that what I need to do is set aside time to pour myself into a creative outlet that isn't bound to budgets, deadlines, brand styles and word counts. Doing this makes me a better writer all around. At the very least, it keeps me from getting worse. That's because it reacquaints me with why I became a writer in the first place, and it gives me room to try new things.
This is true for everyone, writer or not. We all need a hobby or creative outlet - some activity that we can turn to as a medium for the exercise and enjoyment of our gifts. It's the best way to stay sharp.