I think many UCI rules regarding equipment suck, but I don't think UCI can be faulted for the lack diversity or the general resistance to change in road bike design. It is Roadie culture's myopic obsession with pro racing (which is largely controlled by UCI regulations) that is responsible.

As long as every discussion of the merits of bikes and related gear is settle by looking at what the top level pros are using, progress and innovation will be slow, and mostly controlled by UCI regulations and the big names (Shimano, SRAM, etc..).

I find it interesting comparing how things progress with road bikes vs mountain bikes. Whereas road bike evolution is very much a top-down approach (both in terms of the influence of pro racing and of just a small number or bike equipment companies), MTB has been very much the opposite, at least for the past 15-20 years.