UCI only has power on formats [1] used in race. It definitely influences the market but it has no say on which width of handlebar can I use on my own bike as long as I don't pin a number in a UCI sanctionnd race.
[1] I prefer using that word because most aren't really standardised.
And also, not sure how the ratios are today, but 8 years ago, an order of magnitude more people raced bicycles in triathlons than in UCI sanctioned races, where the UCI has no control.
[1] I prefer using that word because most aren't really standardised.