[D] Conference paper is double-blinded. For what?

I am extremely confused by the requirement that papers submitted to conferences must be double-blinded, yet they are allowed to be preprinted with their authors' names and affiliations, and can be shared as the same paper at the same time. People even promote their papers on SNS such as Twitter, LinkedIn, Reddit, etc., before acceptance/publication. It feels like I am watching the Instagram version of academia. How can one ensure that it's the advertisement, rather than the paper itself, that …

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