There are several reasons.
There is more to discuss when it comes to the top characters. They are the characters that determine tournaments for the most part and there's a lot of data on them, which makes discussion more than just a collection of opinions. The BBR (and the community at large) also simply has more high level representation for the better characters, which is logical if you consider tournament placing is often a factor for admission. As you can see from the Diddy discussion and will be able to see in upcoming discussions, there is a lot of controversy regarding the top 5 other than MK's #1 position, within the room itself at least. Getting part of that discussion underway before the actual voting happens will probably prove useful.
It is likely that we will continue the WCD after we do the tier list and finish up what is left, not to mention the fact we will have to order those characters before that anyway. They will definitely get the attention they deserve, but it is a fact that the low tiers do not play a major role in tournament results, aside from the occasional breakout performance. With only two months left and more than thirty characters to cover, this is the choice we made.
I hope this response was useful to you.
