Because those versions are not sold at retail by the studios in every instance. Some are, as in the Radio Disney example I listed earlier, whereas some are not. Just like you cannot go to Barnes and Noble and purchase a psychology textbook with the parts already underlined that Mrs. McScreechy the psychology teacher at Hicksville Community College, will cover in class, but you can purchase at the college bookstore her textbook that a previous student has underlined.
Hicksville Community College ROFL....
The town I used to go to when Billy Joel and my pal Joey Licari used to have battle of the bands back in the 60's! :-)
Getting back to this again. Why do you think those versions you mention aren't for sale to the general public? Because the alterted versions were contracted from the copyright holder for specific viewing. Where we once again delve into copyright laws.
I have to ask, why do you keep coming up with diferent analogies of the same question?