ummm - because no one has figured out how to do it yet ?! lol
if it can be made - it can be dismantled and that is the way of all circumventions. If we knew exactly why we couldent do it then we would also know what to do to enable it.
There is a group of spanish guys working on another method as there have been preliminary reports that you can run unsigned updates via a BDROM v1.1 disc - theoretically it updates the PS without official sony signed code. work is currently ongoing to perpare to dismantle the bd discs when a 1.1 disc containing a feature update and find out what doors can be opened in the ps3os. Certainly the PS3 has been a formidable unit in resisting the barage of hackers thus far, unfortunatly this is making is even more of a trophy achievement for all hackers - especially newer ones that want to cut their teeth and become renowned. Sadly due to the fact that there are so many methods in usage - there is also a lot of people cashing in on work of others, I try to report what the hackers are up to at the moment rather than say anything to excite people unnesesarilly, it will be hacked. and hopefully soon