Interestingly some time back I did an exercise to download data from steemwhales.com. I only got up to around 80k acounts. I messaged the developer of that site and the reason for a much lower number of accounts than registered was
ATM SteemWhales only detects users who voted or posted once
At the time there were over 160k accounts registered. This suggests to me there are a lot of inactive accounts on Steemit, so looking at registered accounts is not very robust metric. Its much better to look at active users.
Active users are very important. Understanding why people become unactive is also important in improving steemit for everyone. I would love to find a way to engage those unactive people, catch them before they drop off....