I used to play WoW years ago and sometimes game lead designer - Ghostcrawler would sometimes share his decision making process. One thing that stuck with me was him justifying removing some gameplay element, it went something like this (I am heavily paraphrasing, it's been like a decade) - players tend to do what gives optimum results even at expense of fun, even if it's a small advantage and to get it is tedious. It is better game design to remove that option so they can do the fun part without feeling guilty about not maximizing their perfomance.
Interesting observation coming from a developer of WoW, a game where people grind for years on end lol. Larian is going that route with gameplay to avoid excessive save scumming interfering with game-flow and immersion.
However, I would argue the character creation isn't really part of the gameplay and thus won't interfere with fun. It's a one time investment if you want, and if you don't, point buy will be a quicker option. The roll method is not only by the D&D rules, it would also be a homage to the original series, both mechanically and as a way to possibly making the player character feel more outstanding and heroic (in BG 1-2 the PC had unique abilities and powers, in BG 3 the PC is seemingly one of several origin characters who share the same abilities and powers). I really hope Larian adds the option to roll and bring on the super-charged tadpole-spawn!
Prof. Dr. Dr. Mad S. Tist 
