According to this entry Number of questions for qualifying in commit stage:
" We increased the requirements to slow down the number of sites that were being created that don't have all that much support to begin with."
Increasing the number of required questions seems like a blunt instrument for reducing the speed at which proposals escaped the commitment phase. But it seems like the target of 40 questions is pretty steep even for some promising proposals, especially since not many users care about Area 51 and the ones that do are limited to 5 questions.
While increasing the number of questions helps make a proposal more mature, why not allow passionate users to create more questions for voting around that proposal instead of just 5.
I believe that some proposals would have a much better chance of making a solid site if there were more questions to vote on. Since Area 51 flipped to the classic up/down vote system from the trinary voting system, there doesn't seem to be much reevaluation on how many questions a person can ask per proposal.
Why not increase the number of questions a user can ask per proposal to balance against all the changes made with Area 51 engine and to help make better proposals?
Those questions will still have to get votes.