Why, until recently, were smooth nose sections not popular? Why, until recently, were smooth nose sections not popular? By smooth I mean without a break between the nose and windshield. (The question focuses on airliners.)

Seeing the Starliner (left) and DC-7 (middle), which were vying for the transatlantic market, with their almost perpendicular windshields, I wonder if they were more slanted and followed the nose -- like the Commando (right), for example, which proves it was possible -- enough drag reduction would have helped their payloads on windy days.

The Commando style windshields only made a comeback with the 787 and A350 -- the 747 gets close, but like the 75/76/777, there is still a break.

Manufacturing difficulty:
I don't think that's the reason (unless proven otherwise), because the noses are already smooth. The nose could start from the top surface of the fuselage, and cut-outs to be made where the windshield panels would go.

Windshield materials:
Plexiglas was used early on and on wartime aircraft with complex curvatures.



Image sources:
- https://imgur.com/iA7tbFV
- https://airandspace.si.edu/multimedia-gallery/dc-7jpg
- http://www.historynet.com/going-commando.htm
Because it's bloody difficult to make the curved shapes out of the materials used until recently, with the technology available at the time.

The few aircraft that had it in the past generally were very expensive and labour intensive to build, compared to competitors, and therefore not economically successful.
Now, with improved manufacturing techniques and materials, plus the rising cost of fuel, it's becoming ever more viable and more such are appearing.