Originally Posted by merlinextraligh

Bikes were originally made of round tubes, with standard sized lugs. That pretty much lead to standardized frame design.

Oversized lugs, and then TIG welded frames lead to some innovation in tube size and thicknesses.

CF lead to all sorts of new possibilities (and to a lesser degree hydroforming for aluminum).

But CF bike frames are an evolving product that's yet to be fully optimized. CF frames started out as round tubes glued into lugs, then molded up frames started coming out, but still pretty much with rounded tube shapes.

Over time, the shape of CF frames has evolved, flared bb's, larger head tubes, boxed sections instead of rounded like a tube.

CF frames continue to evolve and improve, the particular trait you're pointing out is just one more step to try to optimize CF frames.