Not a reason, per se... that's just how point buy works: you start with values of 8, have your point pool to spend, and can't buy an initial value of any higher than 15. It's a boring method of generating that prevents you from ever having any extremes in either direction.
At least Pathfinder let me buy up to 18. Took a ton of points but was doable. With a race bonus, I'd start with 20 in my primary stat >.>
My DM decided that's how we were doing it after I actually rolled 3 18s in character creation....The dice were with me that day.
We did 25 point buy. Not a fan of the system, to be fair. Rolling a 36 point roll though was apparently too much for him. -_-
I remember rolling for hours on BG2 to get optimal stats. Was kinda annoying.
