The driving factor is everything was lower budget.
Marketing was lesser... considering BD had nearly no marketing.
How can a publisher expect growth for a title that had no marketing and sold in spite of them ?
BD sold nearly a million WW and 300k in Japan. Instead of giving it a bigger budget, they did the opposite: smaller budget.
Honestly I think you could take the exact same sequel and have five times the marketing and it really wouldn't see all that much of a boost, especially compared to the expenditure.
Marketing is about getting people to look at a product in the first place to see if they want it, but the product actually has to have lots of appeal in the end. If marketing was a magical salve to everyone's problems, we'd all be using Windows Phones.