The 15 SP gift was costly, and the abuse taking place due to it had to be stopped. I have seen 10s of initiatives to fuel new accounts and don't think that is the reason they didn't stay - @paulag might have something on retention before and after the change - it has always been very poor.
@r00sj3 could well be right, no-one knows for sure. What is pretty clear though is that we have many openly taking their rent home with poor content knowing that in time, others will just follow their lead.
I do like what palnet and steemleo are doing with a centralised account, and as a reasonably good Steem actor, I've long wanted Steemit Inc to take a more active role in policing the network. Some will disagree, and some will disagree that steemcleaners (fueled by 2m SP via Ned) are always right with their downvotes.
We need a change, I'm hopeful this is a positive one.