I’ve seen dozens of innovative designs for making a bike fold up, just so you can take it on the subway and ride the last mile. I have seen only two people using this transportation modality in the last ten years, in two of America’s largest cities. However the predominant bike seen in urban places is the courier special - a vintage road frame with a few gears and a rack or basket.
The urban bikers, in other words, have it figured out. They don’t WANT or NEED another goddamn folding bike. Somebody invent a bike solution for the goddamn suburbs, where people are fat and lazy and take their kids to soccer (wicked mean generalization, sorry…)
And yes, lots of fancy carbon bikes are based on a profile drawing and not much else. It’s the simplest way to iterate a design - and sometimes you get some functional benefits.
UCI weight limit is 6.8 kg, or 14.99 lbs. There are many other obstructions to design as well - aspect ratios of aero tubes, minimum fairings, etc.