I have two points along those lines:
1. Writing software isn't like pumping gas, cleaning hotel rooms, or driving a delivery van. Unless you are a world class genius, even a very slight amount of effort devoted to self-improvement means that you will be able to write cleaner, less error prone, easier to read, easier to maintain, more flexible code every year than you did the year before. If you have zero interest in writing software outside your day job, I can be confident the code quality I get from you today will be the exact same I get from you in five years, ten years, or twenty years and you will be exactly as competent to handle any given task then as you are now. In certain tasks that's fine with me - provided you only ever want salary increases to match inflation.
2. In my own career, I've found that the better I became at writing software, documenting it, designing it, writing tests for it, using source control, setting up development environments, etc.... the more I enjoyed it. I phoned it in at my job from age 24-30, and the only thing that made me improve was getting assigned tasks outside my comfort zone when no one else at the company was available to bail me out. Then in my early 30s, I had a little bit of enjoyment in what I do and started reading Slashdot and Lambda the Ultimate and so forth. Now in my late 30s, I love my work. I may be an awful developer relative to most of the software developer population, I can't judge that accurately. But I am certain my skill today is dramatically superior to what it was five years ago, and in turn that's well beyond where it was ten years ago. So when I see someone that works in this field but never willingly learns new things or discusses ideas beyond exactly what is required for work, I believe in most cases it means they're not skilled enough to enjoy it.
I am not asking anyone to make writing software their sole passion or give up nights and weekends to read on the topic or write code on side projects. I don't do that myself. I read about one non-work-related technology book a year, or take one Coursera class, and tackle a few little personal projects (e.g. setting up a Minecraft server on a VPS for my kids). That is barely a hundred or two hundred hours of work related to my career outside the day job, but the payoff is enormous.