Hi,
Let me explain it :) Steem accounts are not free. Steemit claims accounts with their RC. To prevent people from creating hundreds of accounts they require you to provide email and phone number and then manually verify that you are a real person and has not gotten a free account from them before.
The account creation itself does not take longer than a vote or a follow for example.
Steem.Ninja triggers the account creation as soon as the payment was successful.