Obviously, I don't have any specific insight into the minds of these men.
However, you can see how any governing structure that gives a veto right to a 1/3 minority could easily devolve into gridlock.
Let's say there's a contentious issue. For sake of illustration, let's say it's the blood ban. Let's further suppose that 4 men are currently in favor of repealing it but 3 are against it. The 3 men in the minority might not want to approve any additional GB members for fear that their voting power would get diluted. If they were to add two additional members and it turns out they are in favor of repeal, they'd lose their ability to block the reversal as the vote would now be 6 in favor and 3 against.
Just take a look at the U.S. Congress and how dysfunctional it's become since the senate began requiring routine measures to achieve a 60% approval. And that's just one house of one of the three branches of the federal government.
Trying to run a multi-million member, multi-billion dollar religion by committee, much less by one that requires a 2/3 supermajority vote to implement any major change, is completely ludicrous and likely a major factor in this religion's decline.