The last time I bought a new bicycle, I had to try a lot of them before I found one I really enjoyed. I'd imagine world-class cyclists are even pickier than I am.
Long gone are the days of a pro rider turning up on a relabelled bike of their choice (their bike, their sponsors' logos).
The bikes tend to be distinct enough that they are definitely riding the frame of their team sponsor, and the wheels have become similarly distinctive too (no more Lightweights disguised as Mavic).
Given the choice of 5 high-end bikes and the ability to select a proper size I don't really see a problem.