Indeed, and in fact I see a lot of recumbents in my locale on the longer, flatter bike paths. Not so much in urban traffic. So a bike that's adapted to the human body doesn't mean there's not a better adaptation for some uses.

And I'm certainly not averse to trying one someday -- N+1 and all that. There's a shop in my locale dedicated to them. However, I think the mass market for bikes has diverged from the racing world. Most bikes sold today are of styles such as cruisers, hybrids, and low tech mountain bikes, that are unrelated to racing categories. Even many racing style bikes such as gravel and cyclo are bought with the intention of using them "off label" if you will, just because they look comfortable and rugged. So the UCI isn't holding us back any more.

Hell, there's the whole category of e-bikes. That's probably the biggest threat to the market for more efficient human powered bikes.