Well, that's partly because you've specified "competitive hobbies".
98% of cyclists don't compete in time trials or races. If you single out the 2% of cyclists whose hobby is trying to go faster than the guy next to them, and ask why they buy equipment to make them go faster than the guy next to them, isn't the answer obvious?
No doubt it depends on your location. Cycle commuters in my locale look like [1] - you might see people with TT bars and shaved legs from time to time, but it's certainly not the norm. And if instead of cycle commuters you look at weekend cyclists on scenic bike paths, or the bikes locked to bike racks at major train stations, the vast majority won't be top-price high performance bikes.
It is more of a weekend rider thing, I note theres still only one sit up and beg, to the two drop handled bikes.
Edit:
Just to add, that picture is quite encouraging. People actually cycling in 'normal' clothes, a sign of an improving cycling culture. Hopefully it will spread to the rest of the UK.
why are Scandinavian style bikes, ridden by people in day clothes, seemingly the only acceptable bike commuter to you?
what is it about the look of someone on, say a hybrid, who's wearing gear appropriate to their commute (which may be athletic gear) that induces so much tut-tutting?
98% of cyclists don't compete in time trials or races. If you single out the 2% of cyclists whose hobby is trying to go faster than the guy next to them, and ask why they buy equipment to make them go faster than the guy next to them, isn't the answer obvious?