Actually it has something to do with fees. Steemit pays fees for new members, but sometimes when there are lot of new members, it becomes difficult. There are some services which take money from you and pay fees for your account creation. Or you can ask for help here: https://steemit.chat/channel/help . This is the official chat channel of Steemit. You shouldn't have waited for weeks to enter Steemit. In this channel your issue will be resolved within 2-3 days itself.
It is good to know that, I was trying to understand why some of us got account accepted in the same day, and for others it took weeks! Thank you for sharing this information
But it is not giving an answer to your question.
It is only giving an answer that why there is an acceptance period. It is still a mystery why some accounts get accepted in a day and why some don't for weeks.