Previously, to create an account you would have to pay entire `account_creation_fee` in STEEM.
An account needs to be powered up to be usable.
We do not have transaction fees on Steem platform (which is really exceptional!) but to limit abuse, we are using something called bandwidth.
Bandwidth for transactions is like voting power for voting.
It depends on your Steem Power and by using it too much you get "tired".
By just lowering `account_creation_fee` we would  make that newly created accounts unusable (having too low Steem Power for their bandwidth = too low bandwidth for making transactions)

Currently instead of paying the entire account creation fee with Steem, creators can now pay a smaller fee and make rest be delegated for an account allowing it to start up (post, upvote, etc.). Such account would also benefit from delegated Steem Power as it would be its own (not only for bandwidth, but also for curation rewards, etc.)