Better bicycles are ok? There are all sorts of restrictions for UCI events. Recumbents are immensely faster than upright bikes --- banned. Beam bikes (like trek y-foil) are a bit faster --- banned. There's a lower limit for bike weight. You can't add fairings. You can't add motors or energy storage mechanisms. The stated goal is to maintain the primacy of man over machine and to some extent rider safety. Of course bikes do slowly change over time in ways that are presumably advantageous to their riders, but you aren't allowed to make huge leaps all at once, which makes some sense as it's fine if everyone has the same advantage (but also, pointless and expensive for amateurs).