Passwords:

2 of accounts were made via Steemit and I can confirm that I've not seen master passwords or private keys for those accounts meaning that the master key is probably kept by the accounts that create new Steem accounts on behalf of new people trying to join.

Obtaining Master Keys

I've created two additional accounts via another website and was given private master keys for those two. So, I can recognize the difference. At first, I thought I lost my master key for my first Steem account that I created, which is this one, via Steemit in 2017, but I am pretty sure now that I never got the master key in the first place. I used to ask people about this the past three or so years and I have been confused about the details off and on over the years.

Not Via Steemit

I'm writing all of this for the record to let people know that it would be better to create accounts via other websites. Well, technically, you would need to have a Steem account or at least be sponsored by another Steem account that can create an account for you on your behalf. If you don't do it yourself, you may not get a master key or somebody else may obtain a copy of that master key.

Changing Master Keys

If it is possible to later change your master key, then that might be an option. Making an account on your own might be a bit complex for some people. So, I can understand if people would prefer the easiest way to join or register or sign up possible.