It's impossible for Steem to not be open source. Every node runs the code independently.
https://github.com/steemit/steem
Steemit used to be closed off, but that was two years ago.
https://steemit.com/steemit/@steemitblog/steemit-com-is-now-open-source
So I'm not really sure why you think these things.
Plenty of clones of Steem are around like Golos and Weku. How is that possible without open source code?