2020 numbers from the FAA show that while GA overall had 7,600 hours of personal use, there were 11,854 hours of commercial use in non-Part 135 GA. We can assume that single-engine light aircraft are more likely to be in personal use, but they are also the most common category for instruction, which is the most common commercial use at 5,498 hours. It might seem a bit tautological to say that "a major purpose of GA is train pilots for GA," but GA pilots are the beginning of the career path for on-demand and airline pilots, and the current feeling is that there needs to be more to sustain airline staffing. Major commercial uses of single-engine aircraft include light cargo (especially the Caravan, involved in this case), air medical transportation, and aerial surveying and observation (e.g. railroad and pipeline ROW safety inspection, a very common use of light aircraft where I live). What I mean to say is that there are a wide variety of useful applications of small aircraft, not the least of which is instruction---their second most common application.
The phenomenon you get at has more to do with the historical demographics of aviation. For various reasons that boil down mostly to World War II (which had the effect of a massive government subsidy of both aircraft and pilot training), the cost of entering aviation as a hobby or career has significantly increased over the last decades. Very few young people can afford to obtain a pilot's license and operate an aircraft today, compared to say the 1970s. This is of course a major contributing factor to concerns over staffing levels in the airlines. Similarly, the pace of both development of new aircraft and replacement of the existing aviation fleet has slowed significantly since the '70s. This is most obvious in the fact that a huge portion of the GA fleet today, especially aircraft in personal and instruction uses, were manufactured in the '70s. Both the pilots and the aircraft themselves are aging out, and much of the HN dialog around the issue of leaded fuel seems to miss this point. While the FAA's very slow progress in approval on a 100LL equivalent non-leaded fuel is indeed a problem, I think a much bigger problem is the fact that not even flight schools and charter companies can afford to obtain aircraft with engine designs much newer than the period of a decade after WWII. Unleaded and diesel aviation piston engines are in service right now, but certifying them for use in older aircraft tends to be prohibitively expensive, if it's even practical. The cost increase from a used but current aircraft from the '70s or '80s to a newer design more likely to be trusted on unleaded fuel, on the low end, tends to be a difference between sub-$100k and over-$500k. The argument I am making is that the continued use of leaded fuel probably has less to do with the fuel than with the fact that the current market and regulatory situation in aviation has almost frozen the fleet in time.
There are also obviously concerns about medical certification of private pilots, particularly with the introduction of the BasicMed program which, in practice, makes it significantly easier to hold a pilots license with ongoing medical concerns. Reform of the medical certification system is critical, but it's probably more important that we address the underlying phenomenon that entering aviation as a career has become more and more difficult to such an extent that the average age of professional pilots has consistently increased for decades. Mandatory retirement for commercial pilots was raised from 60 to 65 in order to mitigate this issue, but that was only a temporary fix, and the five years it really bought have long since passed.
All of this said, accidents due to medical incapacitation are actually pretty rare. Bruce Landsberg of the NTSB, in a letter to AOPA Pilot, put it at about a dozen incidents per year in GA... out of around 400 fatal accidents. This actually seems to overstate the problem as not all of those dozen are fatal and the NTSB sometimes ends up attributing loss of orientation to medical incapacitation simply because they couldn't find any other likely reason. For this simple reason, "narcissism" of older pilots is probably not a major contribution to aviation accidents. More philosophically, narcissism is no doubt a contributor to common types of serious and fatal accidents like unintended IMC, but if anything the young are probably the greatest offenders there.