Earlier quoted context omitted.
The whole thing is a fashion show with very narrow limits of what the UCI wants people to do. The rules that ban e.g. the famous Lotus bike were explicitly stated as being meant to discourage wind tunnel testing. Fairings and recumbents have been banned for nearly 100 years because they're too much faster than UCI-style bikes.
It's not about fashion, it's about maintaining an enjoyable and popular sport. 4D chess is probably more "interesting" than regular chess, but people play regular chess because it's a good game that people know and understand. They could start allowing funny looking bikes, maybe off-road sections and, heck, why not an army style assault course? But at that point it's just not the Tour de France any more.
That's an absurd comparison - it's not like we're talking about changing the course or the rules, and it's not like the UCI rules have people consistently using historical-style bikes (they rapidly adopted electric shifting, or novel frame materials, for example). In the world of fencing we have both sport fencing (try to win by whatever means within the rules) and historical fencing (trying to match historical materials, styles etc.) and both those are distinct and interesting disciplines. But adding ad-hoc rules to exclude some innovations but not others, as the UCI does, is the worst of both worlds.