Software development is the only field I can think of where the making of the tools of the trade is wholly encapsulated by the field itself. Maybe blacksmithing. In such an environment, it makes sense. We make our own tools, and for the most part the most powerful of those tools end up being given away for free. To other people who both use the tools, and have the capacity to improve them. Who then give them away for free.

It is not a coincidence that software development tooling is one of the only fields that has has been thoroughly eaten by open source. It's because the user-developer circle is complete. A mechanical engineer probably doesn't have the skillset to improve the CAD program they're running. A software developer probably has the skillset to improve VIM.