I apologize for the lack of foundational knowledge underlying this question.
Initiation of the outward leaders is not well understood. The electric field strength within the thundercloud is not typically large enough to initiate this process by itself.
The above implies that the initiation of outward leaders (and the process by which a charged region of the cloud would cause stepped channels of ionized air to form and branch out towards the earth) would be explicable if the electric field strength within the thundercloud were larger.
Is that interpretation of the wikipedia article correct? That is, are the physical processes that lead to the formation of outward leaders well understood, providing a sufficiently strong electric field exists?
Secondly, my understanding is that in CG lightning, the thundercloud contains both negatively and positively charged regions, possibly created by the collision of different types of ice particles within the cloud. Why would it be easier for the region to neutralize its excess charge with the ground, rather than with the far more proximate oppositely charged region of the same thundercloud?