There's different levels of "open source" (everything from one-way code dumps to full-on maintained-as-a-whole-distributed-global-team). In my experience, it's easier to start with a simple "here's the code, bug reports welcome". This starting point is generally an easier sell to management who's worried about project management taking too much time away from other work.
Like all things, practice, start small, and grow from there. Get's easier as you go. But yeah--licenses/legal, written policies, governance, marketing, time prioritization, and more all take a lot of time to figure out.
NB: My own background in open source biases me to thinking open source is "easy". It's not; it takes a lot of work. The good news is that there's a lot of tools and help available for anyone wanting to start.
I know of many cases where companies wanted to open source software but the plan was nixed when they realized how much it would cost versus keeping it closed. Or companies that did open source their software but the increase in burn rate was not offset by increased revenue.