The transponders are on the bikes because they're not restrictive to the rider that way, and I get that. We see plenty of occasions where a rider doesn't appear in the results or appears incorrectly in the results because the transponder was knocked loose or off in a crash, or they swap bikes during the stage and the organisers didn't pick up on camera to know that domestique Y's bike that crossed the line in the main bunch was in fact being ridden by team leader X. However, transponders are also used in sports like biathlon, cross-country skiing etc. where they are usually strapped around an athlete's wrist or ankle in order to record their position on the course, and while we see tracking errors sometimes when the technology plays up, it doesn't take long for those to be resolved.
Hell, old-time forumers may remember that back in the early 2017 season, there was a very active thread following the Indian-Pacific Wheel Race, an over 5000km ultra-cycling event, where we were following GPS dots marking the locations of riders over the self-supporting event. The event was cancelled after over 90% distance run when Mike Hall, second on the road, was killed in a collision with a car on the road just before dawn outside Canberra. When it was advised to the public a couple of hours later that they were suspending the race and collecting the riders following the death of a participant, followers of the race had been able to deduce that it was Hall that had been killed in a matter of minutes from the transponder data (because the race was being followed almost solely from the transponder data).
Now the India-Pacific Wheel Race was a super-endurance race, with riders extremely fatigued and fending for themselves riding across an entire continent on open roads, riding all hours of the day and night and carrying their own equipment for survival. If a rider's GPS dot stops moving there, they could have stopped to sleep, they could have been stocking up at a cafe, they could have simply needed to rest for a couple of hours. Mike Hall being hit by a vehicle meant that the incident was reported and he was found immediately, but if a rider had crashed on isolated roadway on their own or fallen into the undergrowth or into a ravine or similar, I can understand why it might have taken a long time for the alarm bells to sound. It is unfathomable to me that such an issue would arise at the UCI Road World Championships with its budget, its prominence, a closed course (much of which being a circuit).
Regards the point on the Itzulia and scouting descents though, it is worth noting that the Worlds course here in Switzerland was approved well before the Itzulia incident took place, and for this type of event it's probably a year or two before those changes are likely to see genuine effect.