When licensing something open-source; there should be proof that, within reasonable allowance, that the source should be viewable, downloadable, and modifiable

When licensing something open-source; there should be proof that, within reasonable allowance, that the source should be viewable, downloadable, and modifiable by any customer or person who is aware of the software. I don't get how so many companies say they are "open source" but there's not a single line of uncompiled code available even on request.