I agree with those who have said that this is a move by the wtbts to try and prevent the study articles falling into the hands of us apostates so easily.
Totally disagree with this - think you apostate chaps are getting a bit paranoid & above yourselves! Apostates can (and do) get hold of literature very easily. Kingdom Ministries , elders letters , the Pay Attention book - all are freely available online. The idea that restricting study articles to a 6 million distribution to regular meeting attendees will make it difficult for apostates to get hold of the articles is absurd.
The WTS publishing model worked well when literature was sold - it doesn't when it is given away on a "donation" basis. To mitigate this , inevitably less literature must be produced and the cost of production has to be reduced. Hence paperback books , once a month Awakes , few releases at conventions etc etc. Cutting WT down to once a month should reduce the bottom line by 50 million pounds a year, by my reckoning. JWs are tending to offer 2 WTs and one Awakes at the doors at the moment anyway , so it shouldn't have much affect on donations.