And a few more possible reasons:

The projections probably made assumptions about the distribution of survey coins and other coins that were most likely off.

It was probably assumed that these coins would contribute to growth with some high percentage transferring to growth accounts. That probably didn't happen and instead I have a feeling a good portion of that distribution was either sold or are being held in private wallets  The same for many pre-sale buyers.

I would suspect many private held private wallets probably just aren't staking. It's pretty clear the neucoin didn't think as many people would choose to hold privately and instead would go for the growth account option.