I believe all states should have a road test for elder drivers for numerous reasons, I don't think the point should be why does only IL do it.
The study used the number of licensed drivers in IL compared to the rate of crashes. Comparing the number of licensed drivers doesn't mean all those licensed drivers are out on the road and per the words of the article older drivers aren't out driving as much so that large number of licensed drivers is almost meaningless at that point. I searched the 2021 study (10 months of a time period) and couldn't find that they compared the crashes (per their definition) with the ages of those drivers just compared it to the number of licensed drivers. You could have 100 licensed drivers aged 75 but only 50 of them actively driving and for examples sake let's say half of them get into a crash. That would mean a 50% crash rate. Or maybe 25 of them get into a crash which would be a 25% crash rate.
Crashes from IDOT is defined as
"An occurrence that takes place on public roadways, involves a moving motor vehicle and produces death ,injury or damage in excess of $1,500 person’s property when all drivers in the crash are insured. If any driver does not have insurance, threshold is $500." I'm reading that to mean if it's considered private property it's not counted. A lot of shopping centers for example are considered private property. Now $1,500 isn't all that much these days in terms of damage but it's not capturing all crashes (although hard to do just a qualifying statement).
The study looked at 2021 when the Emergency Rule was in place. That Emergency Rule caused the renewal rates to
increase in time period and
increase the age at which a road test was required from age 75 to 79. It was strictly a pandemic-related thing from DMV backlogs to health risks for elders due to covid. Prior to this once you reached 75 it was a yearly renewal.
For your article you posted IMO it's misleading to me this next statement as if it precludes accidents from occurring:
"Typically, elderly drivers drive during daytime, avoid risky weather and take short trips for necessities like groceries or medical appointments" which I understand is a point to make but that doesn't mean just by doing those things you individually as a person are less likely to be in an accident. Random example I think we've all seen drivers plowing into businesses because they mistook the gas for the brake and it's not all uncommon for that to be elder drivers in the daytime in good weather. Backing into someone is also a common accident. Elder drivers as a whole have an
increased likelihood of declining safe driving. FWIW I think most states start restrictions (in general) at age 65 and up so I don't think the focus should solely be on basically 80 yr and up.
***I'm looking at it from a standpoint of a higher likelihood of decreased driving capabilities from spatial awareness, distance understanding, eye sight and more. FWIW in my state every time you renew your license no matter your age you have to have an eye test. If in person they do it there, if done online paperwork must be submitted reflecting your eye exam results from within a 12 month time period.
In any case totally far off the topic of quirky state laws so I'll leave it there
Hopefully your next driver's test goes well
Not to be out-done, she sang it again. It turned into a looong opera! 
