I haven't made that transition, but I can say from experience that (for me, at least) hobbyist side projects are a lot different than working on software full-time. When you're coming up with your own side-projects or picking FOSS to contribute to you get a lot more freedom in what you're doing and how you do it than if it's handed down to you filtered through managers and other more senior engineers. Unless you're lucky, there's a good chance you'd end up working on something that doesn't really interest you or stimulate you in the way that solving your own problems can.

That being said, I work full time on software that doesn't always align 100% with my passions, but it hasn't dulled my interest or excitement in programming in general or my side projects at all.