And that's great and all, but it also ensures that the only thing you did that was noteworthy for prospective employers was whatever project you happened to be stuck with your current job.
If you happen to be privileged and work on architecting exciting cutting-edge projects that use any of the relevant or even popular technologies then you have nothing to worry about.
If, instead, you happen to be like the most of us and are working on maintaining legacy projects with technologies that you hate and are obsolete and became irrelevant to the eyes of prospective employers, or even worse you are stuck on doing boring stuff that tangentially have anything to do with development at all... Then how do you work on your marketable skills?
Do you honestly expect to be the best candidate to a job position when you're competing with people who spent years working on exciting and interesting cutting-edge technologies when all you have to show for is years of maintaining a legacy application that was mostly done except with the minor updates you were charged to do?
So yeah, please do enjoy spending all your free time playing with your kids. Some of us are compelled to, in the very least, brush up their skills outside of work because otherwise we might not have a shot at a job that allows us to play with the kids, or even get a job in the near future.
Your line of reasoning doesn't actually benefit you unless you can negotiate a higher wage because of your side projects. In most cases, it's a proxy for an employer getting away with not paying you for training - either your current employer or a prospective new employer.