It seems like every week there is at least 1 small aircraft that crashes that kills several people.
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Seems, madam? I know not
seems." I know of no statistic which suggets the number of GA accidents is up. On the contrary, every statistic I've seen from the FAA says they're down, both in rate per flying hour and total numbers.
Is it because the planes are unreliable?
Again, on the contrary, all the accident statistics suggest that accidents due to mechanical/material failure are decreasing progressively.
The weather hasn't changed much over the last hundred years. Again, if anything, the number of weather-related accidents is down, probably due to improved weather reporting/forecasting technologies, better weather information distribution systems, improved aircraft capabilities, and pilot education.
Or that they pilots are doing stuff out of their league or jurisdiction?
The biggest cause of light aircraft accidents is pilot error, in the form of either bad decision-making or weak piloting skills ("stick-and-rudder" skills).
I know there is a statistic out there showing that airplanes are safer than cars
A bit misleading. Air carrier safety is much better than road vehicles, and professionally flown aircraft (business and commercial) are not far behind air carriers, but accident rates for nonprofessionally-flown light planes are about the same as motorcycles, and worse than private autos.
Can't say -- where did you get the idea that aircraft accidents are up?