'Purchasing' a beta code? Does Activision's greed hold no limits? Once upon a time, long, long ago (at least it feels like it) a Beta was a chance for developers to fine tune their game or spot any critical bugs. Previously these tests were closed, either to close friends or relatives of the developers or perhaps people well known to the Publishers as a way to increase publicity but as games became more complex the need to get more testing done to spot and iron out bugs became more apparent. So open or public Beta's started to appear. After all even if 100 testers play for a hundred hours each that number is a drop in the ocean compared to getting 100,000 people to play your beta for even ten hours in total.
Then publishers realised Beta events were also a great way of building a major hype machine and getting people excited across forums and social media so many 'beta' programs were evolved into what used to be known as Demos. A chance to sample the game prior to launch and often these beta builds were actually pretty close to how the game would launch in a couple of months time, severely limiting any chance to change the game majorly or crush any minor, annoying bugs.
Then some bright spark, probably within Activision, thought 'if the demand is there, I wonder if people will pay to be in the beta? Lol they might even think we'll listen to their feedback and even let them fight each other on an 'official beta forum' while completely ignoring them so they think they're shaping the game!' And, sure enough, some (well, a lot by the looks of it) misguided souls paid a few pounds to be involved in 'testing/money grab' and found themselves suckered into a game they may only get to play for a few days and then be deleted forever, and then still have to pay full price for when it is released, likely with the same game breaking bugs that were spotted in the testing but couldn't be fixed in time for the hard-set launch date.
TL;DR, a fool and his money are easily parted.