Absolutely true. You can find articles in the 80s in Dragon magazine where they talk about creating backstories for your characters as an important roleplaying enhancement. And there were plenty of not-D&D games where that advice was given as well where it would bleed over into D&D if you played them.I'm going to disagree with the idea that long backstories for characters is some new development. When I ran 1e back in the 80s, my players would create genealogies connecting their characters, their ancestry. I have zines from the 80s and 90s that have whole sections dedicated to character backgrounds. Somewhere I have the two-page backstory a player handed to me for their first level halfling in 2e.
IME the number of players who would show up with a 12 page backstory for their character was small, but it wasn't zero. In fact I think these days backstories among the folks I play with tend to be shorter because there are some explicit rules in place for shorthand about backgrounds in the games we play (13th age in particular reduces the 12 page backstory down to a few background tags you can come up with for yourself to get some bonuses on skill checks and a One Unique Thing that should be about a sentence or two. You can still work a 12 page backstory up if you want to, but who has the time these days?)