I suspect it's connected to the fructose trigger we all have; this sets fat cells to 'store' mode, and is involved in metabolic water production for scarce potable water (e.g. marine mammals) and low O2 survival (e,g, naked mole rats). https://onlinelibrary.wiley.com/doi/full/10.1111/joim.12993

I've learned (pretty sure it was in one of the Peter Attia podcasts with Thomas Dayspring, AKA "Dr. Lipid) that a large surge in serum sodium can make us create fructose and so trigger the reaction.

I've also read that African Americans, but not Africans in general are 'salt sensitive'. A somewhat obvious reason might be the "middle passage" that many enslaved Africans endured in which the ability to store fat and to convert stored fat to metabolic water would have had a survival advantage.

This is a bit of a leap, but it might explain why for some of us, salt might be connected with weight gain and hypertension.

I'd also guess that nutritionists of the day didn't know that low salt could be detrimental for the rest of us.

Disclaimer: I too am something of a salt hound. Every year, my blood work indicates my sodium is at the lowest-normal level or a bit below - in spite of all the salt I consume.

Oh, one of the other issues with salt restriction is that it's also a chloride restriction - and chloride is one of the components of hydrochloric (stomach) acid.

Finally, If you're interested in this area and not sure where to start, check out Peter Attia's "Drive" and Rhonda Patrick's "Found My Fitness". Both have websites, youtube videos and audio podcasts of those videos. (reason I'm not 100% sure where I learned about sodium/fructose; a car in motion is a terrible place to take notes)