Still doesn't explain why it's all not at least source-available. I'm not going to complain if they don't use open-source licenses such as MIT or (A)GPL, but straight up not making the source code publicly readable at all is a big strike against it.
I see no reason not to do this, especially for such a security-oriented service. You should be striving for as much transparency as possible.
Where is the repo of software that you've paid an unknown number of developers to work on for multiple years over multiple versions that you charge for and run a viable business employing all of the peoples?
That's why every "the company source code got stolen!" news is nothingburger, no competitor can use it, it would be huge liability to be caught using it, and it "only" matters for people that might find bugs in it.
https://github.com/bitwarden/server/blob/master/LICENSE_FAQ....