Mainly because that stuff is pirateware, isn't it? If not Red Hat would be carrying it in their complete distribution of GNU/Linux, don't you think?
If I buy a DVD I have the right to view it on my home computer. I do not have the right to publicly broadcast, copy for resale, etc. I do have the right to make personal copies for backup. I do have the right to take excerpts for a review.
This "pirateware" allows me to do all that. Yes, I know it can be used for illegal copying, but then a gun can be used for illegal killing too. Should we ban guns?