If "good for business" was the concern, I would have thought a change that caused them to lose 30% of their D1 coaches would have made someone wake up and ask questions.

I've always wondered - Is Seble the only decision maker on how HD changes?  Or do those decisions get vetted through a group of people?  Or is he just the messenger/main developer who follows the guidelines put forth by others?

Does anyone have the latest stats of humans per division?

I'd argue that DI is empty because HD is empty .....in all divisions.      So if the heavy BCS weighting is killing interest in DI how would you explain the dead interest in DII and DIII?

I'd argue that they are two separate problems although the first dramatically impacts the second.

In a model like this, D3 and D2 are mostly the domain of the new (D3) and up and coming customer (D2).  You know you will lose a percentage of them as they try the game and tire of it but you know a certain percentage will become long term customers in your D1 worlds.  Sure, some people will not try to progress but that will not be the majority of the customer base and you build in a fudge factor for those customers in your planning. 

So - Why are they not attracting new customers that are working their way up through D3 and D2?

D1 suffers if you aren't bringing in new customers because even in a well run game there will be some loss of D1 coaches.  Those losses need to be made up for by the newly arriving D2 "graduates".  Fewer D2 graduates, fewer new D1 coaches to replace the regular loss.

Add in that D1 decisions have made many D1 coaches leave the game (or at least D1) at a greater rate than would be normal and you now have an even greater need for D2 graduates (which as you have said don't exist).  It could even be theorized that D2 coaches that have in the past thought they would move up see the number of D1 coaches moving down and decide it's not worth it since they face a long, long, long road before they can hope to win even a single game in the NT.

Many companies find it useful to have a pipeline metric when determining where they are today and where they are likely to be tomorrow.  For example, if you know that for every 100 new D3 coaches, 50 of them will make it to D2 and eventually 20 of them to D1, that allows you to see what is in your pipeline and you can make rational decisions on how to manage your product.  If you find you are losing D1 coaches at a greater rate than expected you can review the reasons why but also see if this is a real problem that requires action or something that will work itself out because your pipeline is full enough that the losses will quickly be replaced.  This sort of stuff is just data and easily mined if a company cares to understand its product.  I doubt anyone considers this important enough though.  I think WIS as a whole is probably just a minor cash cow and HD is even less of a concern to anyone but the people who play it.