Because you can pick your nose, but you can't pick your Orbiter Add-on's Distribution License.
To use this tool, simply fill out the form, push Evaluate, then complain on the forums when the result isn't what you were told you wanted. For questions of the form "Does your add-on X...", if it presently does not X but you plan for it to X in the future, answer affirmatively.
NOTE: This tool is intended for new add-ons that have not yet picked a license. If you already released under another license, consult the forums for guidance and/or abuse before continuing.
SURVEY QUESTIONS:
Does your add-on have a program or DLL?
Do you want to share the source code of your add-on?
Is it OK for others to modify your add-on's source code and distribute their modifications?
Is it OK for others to use your add-on's source code in their own open-source projects?
Is it OK for others to use your add-on's source code in their own closed-source projects?
Is it OK for others to use your add-on's source code in their own commercial projects?
Things such as documentation, meshes, textures, sounds, and configuration files that are not program source code are called assets.
Does your add-on have assets?
Is it OK for others to modify your add-on's assets and distribute their modifications?
Is it OK for others to use your add-on's assets in their own open-source projects?
Are you OK with distributing the Photoshop/Blender/3DSMax/etc. files used to make your meshes/textures/sounds?
Is it OK for others to use your add-on's assets in their own closed-source projects?
Is it OK for others to use your add-on's assets in their own commercial projects?
Is it OK for others to distribute copies of your add-on?
Is it OK for this to be distributed in a bundle with other similarly licensed add-ons?
Is it OK for this to be distributed in a bundle with other differently licensed software?
Is it OK for others to charge money for distributing this?
Does your add-on INCLUDE anything copied from another project? (Things that you USE but do not INCLUDE, such as the Orbiter API or OrbiterSound, do not count.)
Please describe all of the items your add-on includes that were not created by members of your project.