Not just that, but a lot of the money in cycling comes from bicycle (+bike component) manufacturers in the form of sponsorship and endorsements. Outside of a NASCAR-like pseudo-standardization, going to a standardized bike from one manufacturer for the highest-visibility events would throw that money out the window (and cause conflicts where the biggest riders are riding bikes from a different manufacturer than the one that funds the rest of their activities).
I understand that's the way it is, and I understand the power/money systems are set up in a way that no one realistically has the ability to make the change happen, but that's not intrinsic to the sport, it's just something that's grown up organically around it.
