This is very off-topic and for that I apologize, but can anyone shed some light on why so many texts of this era use 2 backticks/graves as a left double quote a

This is very off-topic and for that I apologize, but can anyone shed some light on why so many texts of this era use 2 backticks/graves as a left double quote and 2 apostrophes (neutral single quotes) as a double right quote? I could understand using neutral single quotes all around if the double quote character wasn't available, but why the backticks? I get that they look more out of place with proportional fonts than fixed-width, but even when fixed-width was ubiquitous and even if this usage of glyphs looked symmetrical, it would've deviated from how the code points are defined, right? Or were the definitions so multi-valued (like the "hyphen/minus" character) that this was legitimate?