Its strange how people say there's no one true way but there are better ways than others. The existence of BIFTs as they are, is just another "way."
BIFTs are short, sweet, and out-of-the way. They're not rails to enforce your character nor drawn-out explanation of character quirks, they're handrails.
Obviously, those attuned to roleplay will be better at it and not need handrails, they've practiced! But, not all players are putting in that much time into practice yet still want to feel like they understand their character.
When you are stumped for how your character would react, you need only to read 5 sentences and get back on track, not your backstory and not your class features. This is what drives the personality traits.
They're meant to be a compass, not a map.
I'm not sure this is a practiced or unpracticed thing. BIFTs as roleplaying aids are fine, I suppose, but I'd prefer them to be less tropey and obvious in presentation if that's the case -- actually make the player think about what they want their character to be rather than some randomish lists of things they can pick and ignore however they want.
I mean, take Blades in the Dark -- there's less space on the sheet devoted to looks, heritage, background, and vice, but these things are massively influential in play. Because they're levers -- they're things that play can revolve upon, and also because you get to mark XP if they cause you issues/come up often in session. Take my game from last night, where a rogue ghost of a vanquished rival (Ulf Ironborn) crashed a negotiation I was in. Happens both the ghost and I were Skovlander heritage, which is a strong part of how that rivalry started. I leaned into heritage and used that as part of my attempt to banish the ghost (in addition to a playbook ability), which reminded everyone at the table of who we were as characters -- Skovland -- and the baggage that comes from that (my action was to command to ghost to abandon it's quest because it's just another in a line of failures -- Skovland lost against the Imperium, Ulf lost against us, and his spectre will lose again). This also hit my background, since I was a rebel in Skovland but abandoned that fight when I realized it was hopeless.
One line on my sheet, not even a sentence, taking up less space than a Trait, both helped define the course of the game (how and why we engaged Ulf to begin with) and continues to have impacts in play on a session by session basis. My character's heritage isn't something to be ignored, it's defining, and I'm rewarded for leaning into it.
BIFTs have none of this. They are, as you note, there for occasional consideration when you don't have a better idea of what your character does. This is my issue with BIFTs -- if this is the height they aspire to, the bar is so low as to be trivial. If, instead, they're actually meant to do more, to actually impact play and be a thing play is about, then, well, they fail utterly at this goal. I've run games and, after a few levels in, looked at BIFTs on character sheets for the first time, and been like "where has this been?" And this was running with a houserule that players can invoke their own BIFTs for immediate Inspiration on the current action without needing GM approval, just a description of how it works. And these are players that dug in deep to Blades.