It was never publicly proposed. When was it proposed, and by who? It's not been seriously debated by Congress.
Some states listened and intentionally dragged their feet. Mine is one - we needed an extension in order to fly -- but we're rolling it out here now too.
Funny you should mention that in your call for caution against black pilling. When SS was proposed there was massive popular outcry against serializing citizens with a federally assigned number. The USG assured everybody that SSNs would only ever be used for the distribution of benefits...