I think the problem is that that kind of work requires a good deal of developer resources for a long time. What company wants to pay upkeep on a shipped product? You could save hundreds of thousands of dollars a year by shipping a rootkit to players and not worrying about server security.
It only needs to be good enough that people keep buying (or not) the Prime when their old account gets banned. There is good reason that it exist, also from cheating perspective.
