I suspect using triathlon bars exceeds the performance of every tested position. Unfortunately there are not allowed by the UCI for inline races. Progress is very slow in some areas ...
It's the same for many sports. You could use aluminum bats in major league baseball. They don't because they simply work too well. In addition to killing the pitcher if you hit a line drive at him, every hit would be a home run. They'd have to make the stadiums larger and add more outfielders. Why bother? Then they'd make the bats even more powerful, and the process would repeat again. So they just use wood bats.
There are plenty of opportunities to race streamlined recumbent bikes, by the way, it's just not the ruleset in play for the Tour de France. (And of course you can use a TT bike in the time trials.)
1) Increased safety
2) More entertaining racing (not much success here so far)
3) Reducing the cost so that it is economically sustainable even for smaller teams.
Still, the current cars are the fastest F1 cars ever.
See DAS this year, F Duct in the early 2010s, the 2009 Double Diffusers (when they were technically banned), Blown diffuser, CF layups that cause the front wing to flex under load etc. etc.
The Mercedes F1 DAS system they intend to race this year when the season gets underway is just the latest example, but see also the 6 wheeled car, the fan car, getting around the ground effect ban, double diffuser, blown exhaust etc. etc.
It's one of the reasons I love the sport.
As others have mentioned, F1 is probably the closest today.
There is a good answer to this question here:
https://bicycles.stackexchange.com/questions/10231/why-dont-...
Cycling has some dumb rules (e.g. sock length), but banning aerobars in mass start races is not among them.
However, full-size tri/TT bars aren't even allowed in triathlons where drafting is permitted. Only recently have reduced-length aerobars been permitted in drafting-allowed races (aerobars no longer than the drop bars/hoods).
Full Tri/TT bars aren't allowed in UCI races because they poke out in front of the bars and hoods; there is some concern they could stab someone in a crash. UCI races allow drafting. The shorter aero bars are relatively new and there is certainly some resistance to change in UCI. I don't know how long it has been since UCI reduced the minimum weight limit but it's been 6.8 kg for quite some time.
Additionally, tri/tt bars reduce your steering stability, which is potentially very bad on a fast descent like this. Usually tri/TT bars do not have brakes on the extension arms — neither for clip-on aero bars for road bikes, nor dedicated tri/TT handlebars.
Anyway, I have aero bars myself and ride in that position going fast on flats and modest descents. But I go back to a wide, near-the-brakes position above 30 mph.
Both times I hit 55mph, and the bike was rock solid riding at that speed on the aero bars.
The fastest descents I’ve done without tri bars has been in the 45 mph range, but I’m sure faster is possible with the right hills.