Blender itself is also over 20 years old. And it struggled a lot even when opt source until several things came together at once. A mix of a UX overhaul, autodesk pissing off the community, and outreach yielding fruit as corporations experimented with adoption.

I'm not sure if we had that perfect storm in game engines yet. Unity fumbled big time, but Godot wasn't quite mature enough to fully take advantage of that opportunity.

>Just freeing your product might not get you enough traction by itself.

Plus not everyone wants to give their product away. I see that advice all the time here and reddit and other places, "just opensource it" as if that's a solution to every problem a creator might have. I even saw it on a gamedev subreddit where a guy was asking how to make more money and people were saying to make it opensource, as if making it free would somehow increase sales for him.

Clearly you are unfamiliar with the process. Step 1, open source project. Step 2. Step 3, profit.