I've never understood the point of a fixed-point system - I guess it's got something to do with wanting to make an egalitarian point or sometihng like that, but that wasn't the idea of rolling stats to begin with, the idea was to take the "God given" roll and live with it, make the best of it, and then the idea of re-rolling came in to get better rolls for min-maxers.
Fixed point is easier to balance.
As you know that no-one will be running around with a god-roll, and no-one will be running around with a trash roll.
This also goes alongside the hard locks on stat adjustments - Here in BG3 you can't put your starting stats below 8 or above 15 (Without the "Racial bonus" addition). To further streamline balance concerns (For example, most jumps in BG3 can be made by a character with 8 Strength, so a character is never screwed by their inability to cross a gap even if they don't utilize any other means to boost themselves).
It's generally a video game themed design. Since, in TT games, the DM can (And will) adjust things to ensure that players can progress and have fun irregadless of if they're min-maxing or playing some jank roll build. While a video game cannot adapt to each player in the same way, so they have to figure ways to streamline players into a more narrower experience that they have designed.
This is also why the dice based systems are fun in TT, because things like crit fails and nat 20's can add to the experience whilst the DM will adapt to ensure that the game is still fun. While in video games dice RNG can be frustrating because the extremes not designed for and can't be adapted to by the game itself (Heck, I remember rage quitting Xcom during the TUTORIAL because I kept missing every 95% shot and taking 5% hit crits. It took some years before I went back with better RNG and actually really enjoyed the game when getting more reasonable rolls)
