Apparent pedal force improvement from swept back handlebars; why not use them? As a teenager a friend found some antique swept back motorcycle handlebars that had the same expansion nut type fitting as my bike and we had to try them out; the handles just touched the front of the saddle when turning very sharply - with any kind of speed, not at all. The point is the amount of force that could be applied to the pedals was greater, because pulling up on the handles was close to being in line with the force down. As analogy, it was like lifting a weight in a straight line from standing above position instead of having it out at arms length and trying to lift. My father immediately ordered their removal as unsafe - it certainly made it (too) easy to wheelstand both from centre of mass being further back (upright position) and that greater force. However, if a bike were designed to achieve that in line pull on handlebar/push on pedals, would performance, especially uphill/against the wind be improved?  I think recumbent designs may use this effect.
For one thing, the aerodynamics are terrible. For another, most cycling is not dependent on peak power, but on sustainable power, for which leg strength (or body strength) isn’t as important as cardiovascular capacity.
Some recumbents do use bars like the ones you mention, but the geometry is so different that muscle recruitment is also very different.