I think you've just claimed it again?
> I specifically ask why would it matter if you knew about other offers? If you are okay to work for 30K then why you are suddenly not okay if you learn that somebody else gets paid 50K at the same company?
If you learned you were paid %30 less than everyone else at your level, wouldn't you go for a renegotiation with your manager or go back to the labor market? Would you internalize that difference as "I guess the company knows my worth exactly and I deserve it"? If you knew the average price for your level as a candidate, wouldn't you use that knowledge in your next negotiations? I mean, I thought this was common sense, self-explanatory game theory. You are claiming the knowledge of the competing price points to have zero value in price setting, and it is a strong claim that requires matching evidence.
> I get spammed with a lot of European jobs on LinkedIn (I have no idea why they would shop for programmers in the US to be honest), none of them have fixed salaries
Your personal sample is hardly representative because we are trying to establish existence of transparently priced positions that are not low-skilled. From the top of my head, if you have access to paper version of 'The Economist', you will see plenty of such ads. Granted, this might be my availability bias, but definitely there is no hard rule of concealed pricing for highly skilled jobs.