When you choose the upload tab in Insert > Media dialog, it says, If you do not own the copyright on this file, or you wish to release it under a different license, consider using the Commons Upload Wizard." But it doesn't say what the proposed license is. Consequently, it's impossible for the user to know whether s/he wants a different one before clicking on anything else.
Please display the license somewhere inside that dialog box, during its initial/nothing clicked on state.